SlideShare a Scribd company logo
 Endocrine System
• The endocrine system is a chemical messenger system
comprising feedback loops of hormones released by
internal glands of an organism directly into the circulatory
system, regulating distant target organs.
• In humans, the major endocrine glands are the thyroid
gland and the adrenal glands.
• In vertebrates, the hypothalamus is the neural control centre
for all endocrine systems. The study of the endocrine system
and its disorders is known as endocrinology.
1JCR - Endocrine System
2
Intercellular Chemical Signals
• Hormones: type of intercellular signal. Produced by cells of endocrine
glands, enter circulatory system, and affect distant cells; e.g., estrogen
• Autocrine: released by cells and have a local effect on same cell type
from which chemical signals released; e.g., prostaglandin
• Paracrine: released by cells and affect other cell types locally without
being transported in blood; e.g., somatostatin
• Pheromones: secreted into environment and modify behavior and
physiology; e.g., sex pheromones
• Neurohormone: produced by neurons and function like hormones; e.g.,
oxytocin
• Neurotransmitter or neuromodulator: produced by neurons and
secreted into extracellular spaces by presynaptic nerve terminals;
travels short distances; influences postsynaptic cells; e.g.,
acetylcholine.
JCR - Endocrine System
 Functional Classification of Intercellular
Chemical Signals
JCR - Endocrine System 3
4
 Functional Classification of Intercellular
Chemical Signals
JCR - Endocrine System
 Hypothalamic Control of the
Endocrine System
• Master control center of the endocrine system
• Hypothalamus oversees most endocrine
activity:
– special cells in the hypothalamus secrete hormones
that influence the secretory activity of the anterior
pituitary gland
• called regulatory hormones
• releasing hormones (RH)
• inhibiting hormones (IH)
• Hypothalamus has indirect control over these
endocrine organs.
JCR - Endocrine System 5
JCR - Endocrine System 6
 Hypothalamic Control of the
Endocrine System
• Hypothalamus produces two hormones that are
transported to and stored in the posterior pituitary.
– oxytocin (paraventicular nucleus)
– antidiuretic hormone (ADH) (supraoptic nucleus)
• Hypothalamus directly oversees the stimulation and
hormone secretion of the adrenal medulla.
– An endocrine structure that secretes its hormones in response
to stimulation by the sympathetic nervous system.
• Some endocrine cells are not under direct control of
hypothalamus.
JCR - Endocrine System 7
JCR - Endocrine System 8
9JCR - Endocrine System
Pituitary gland
10JCR - Endocrine System
The master gland :
• The pituitary gland is called the “master gland”
because its hormones regulate other important
endocrine glands—including the adrenal, thyroid, and
reproductive glands (e.g., ovaries and testes)—and in
some cases have direct regulatory effects in major
tissues, such as those of the musculoskeletal system.
11JCR - Endocrine System
12JCR - Endocrine System
 Anatomy
Location
• Lies at the base of brain Sella turcica.
• Connected with the hypothalamus by the pituitary
stalk or hypophyseal stalk.
Division
• Anterior lobe ( adenohypophysis)
• Intermediate lobe ( not present or very small in
humans dispersed within anterior lobe)
• Posterior lobe ( neurohypophysis)
13JCR - Endocrine System
 Lobes of pituitary gland
• Anterior pituitary ( adenohypophysis)
Consists of three divisions
1. Pars distalis
2. Pars tuberalis
3. Pars intermedia
• Posterior pituitary
Consist of two parts
1.Infundibular stalks
2.Pars nervosa
14JCR - Endocrine System
15JCR - Endocrine System
Pituitary hormone secretion
16JCR - Endocrine System
Pituitary Gland (Hypophysis)
• lies inferior to the hypothalamus.
• Small, slightly oval gland housed within the
hypophyseal fossa of the sphenoid bone.
• Connected to the hypothalamus by a thin stalk, the
infundibulum.
• Partitioned both structurally and functionally into an
anterior pituitary and a posterior pituitary.
– (called anterior lobes and posterior lobes)
JCR - Endocrine System 17
The pituitary gland consists of:
A) Anterior lobe (adenohypophysis): Consists of:
- Pars distalis - Pars tuberalis - Pars intermedia
B) Posterior lobe (neurohypophysis):
Consists of pars nervosa which is connected by
infundibulum (pituitary stalk) to the median
eminence (tuber cinereum) of hypothalamus.
JCR - Endocrine System 18
Pars distalis is formed of:
Thick irregular cords of cells + blood sinusoids
There are 2 types of cells:
a) Chromophobes: About 50% of the cells. They are
small, found in groups and have NO GRANULES in
their cytoplasm.
b) Chromophils: The other 50% of the cells. They have
GRANULES in their cytoplasm and are larger than
the chromophobes.There are 2 types of chromophil
cells:
— ACIDOPHILS (10%): have reddish cytoplasm. They
secrete growth hormone (GH) & Prolactin
(lactogenic) H.
— BASOPHILS (40%): have bluish cytoplasm.
They secrete TSH, ACTH, FSH & LH.
In general basophils are larger in size and stain deeper
than the acidophils.
JCR - Endocrine System 19
Cells and hormones of the anterior pituitary gland & their functions
Cell Hormone secreted Function
Somatotropes
(Acidophilic)
Growth H (somatotropin) Stimulates body growth
Mammotropes
(Acidophilic)
Prolactin (PRL) Stimulates milk production &
secretion
Thyrotropes
(Basophilic)
Thyroid Stimulating H (TSH) Stimulates production of thyroid H
by follicular cells
Gonadotropes
(Basophilic)
-Follicle Stimulating Hormone
(FSH)
-Luteinizing H (LH)
-Stimulates follicular cells in ovary
& spermatogenesis in testis.
- Stimulates production of estrogen
& progesterone from the ovary &
testosterone from the testis
Corticotropes
(Basophilic)
Adreno-Cortico Trophic H
(ACTH or corticotropin)
Stimulates secretion of
glucocorticoids & androgens from
adrenal cortexJCR - Endocrine System 20
Pars nervosa contains:
a) Bundles of nerve fibers.
b) Cells called pituicytes.
c) homogenous intercellular
substance: on fixation it
precipitates to form
Herring’s body.
• The bundles of nerve
fibers in the pars nervosa
arise in the hypothalamus
and descend to the
posterior lobe forming the
hypothalamo-
hypophyseal tract (HHT).
• The hormones secreted
by nerve cells in the
hypothalamus travel
down along the HHT &
accumulate at the end of
the tract in pars nervosa
as Herring’s bodies.
• It secretes Vasopressin or
ADH (Anti Diuretic H) &
Oxytocin.
JCR - Endocrine System 21
JCR - Endocrine System 22
 Pituitary Gland Blood Supply
JCR - Endocrine System 23
 Seven Anterior Pituitary Hormones
1. Human growth hormone (hGH)
2. Thyroid-stimulating hormone (TSH)
3. Follicle-stimulating hormone (FSH)
4. Luteinizing hormone (LH)
5. Prolactin (PRL)
6. Adrenocorticotropic hormone (ACTH)
7. Melanocyte-stimulating hormone (MSH)
JCR - Endocrine System 24
JCR - Endocrine System25
Posterior Pituitary
JCR - Endocrine System 26
Figure : Synthesis, storage, and release of posterior pituitary hormonesJCR - Endocrine System 27
Posterior Pituitary
– Antidiuretic Hormone (ADH)
• Causes kidneys to retain more water
• Causes vasoconstriction  increases blood pressure
• Dehydration, pain, stress  increase ADH secretion
– Oxytocin causes
• Smooth muscle contraction of uterus during childbirth
• Causes “letdown” of milk from glands to ducts
JCR - Endocrine System 28
 Posterior
Pituitary
JCR - Endocrine System 29
JCR - Endocrine System 30
 Pituitary gland disorders
Causes of disorders of pituitary gland
• Hyperactivity
• Hypoactivity
Hyperpituitarism
• Hyperfunctioning of anterior pituitary gland -
Gigantism and acromegaly
• Hyperfunctioning of posterior pituitary gland -
Inappropriate release of ADH
31JCR - Endocrine System
 Hypopituitarism
• Hypo functioning of anterior pituitary
Dwarfism.
• Hypo functioning of posterior pituitary
Diabetes insipidus
32JCR - Endocrine System
 Gigantism
Characterized signs and symptoms :
• Excess Growth of body
• Average height is approximately 7-8 feet
• Headache due to tumor of pituitary
• Hyperglycemia, visual disturbance and pituitary diabetes
mellitus.
• Cure : Gigantism can be cured by hypopituitarism ( burning
cells of anterior pituitary)
33JCR - Endocrine System
34JCR - Endocrine System
 Acromegaly
Characterized symptom & causes
• Enlargement, thickening and broadening of bones.
• Particularly extremities of the body.
• Hypersecretion of growth hormone, thyroid,
parathyroid hormone.
• Hypertension, headache and visual disturbance are
seen.
• Cure : as like as gigantism.
35JCR - Endocrine System
 Dwarfism
Deficiency of
growth hormone
in children before
growth is
completed
resulting retarded
growth.
• Short stature.
36JCR - Endocrine System
 Control of Anterior Pituitary Gland
Secretions
• Anterior pituitary gland is controlled by
regulatory hormones secreted by the
hypothalamus.
• Hormones reach the anterior pituitary via
hypothalamo- hypophyseal portal system.
– essentially a “shunt”
– takes venous blood carrying regulatory hormones
from the hypothalamus directly to the anterior
pituitary
JCR - Endocrine System 37
JCR - Endocrine System 38
39JCR - Endocrine System
Thyroid gland
40JCR - Endocrine System
Thyroid Gland
• Located immediately inferior to the thyroid cartilage of the larynx and
anterior to the trachea.
• Distinctive “butterfly” shape due to its left and right lobes, which are
connected at the anterior midline by a narrow isthmus.
• Both lobes of the thyroid gland are highly vascularized, giving it an intense
reddish coloration.
• Regulation of thyroid hormone secretion depends upon a complex thyroid
gland–pituitary gland negative feedback process.
JCR - Endocrine System 41
Thyroid Gland
• Follicle cells:
– Produce and secrete thyroid hormone
– Precursor is stored in colloid
• Thyroid hormone
– Increases metabolic rate
– Important in growth and development.
• Parafollicular cells
– Produce and secrete calcitonin
• Calcitonin
– Secreted in response to elevated calcium levels
– Reduces blood calcium levels
– Acts on osteoblasts.
JCR - Endocrine System 42
JCR - Endocrine System 43
JCR - Endocrine System 44
JCR - Endocrine System 45
The thyroid gland produces 3 major hormones:
• Calcitonin: Reduce the concentration of calcium ions in the
blood by aiding the absorption of calcium into the matrix of
bones.
• Triiodothyronine (T3)
• Thyroxine (T4)
The hormones T3 and T4 work together to regulate the body’s
metabolic rate. Increased levels of T3 and T4 lead to increased
cellular activity and energy usage in the body.
46JCR - Endocrine System
47JCR - Endocrine System
 Thyroid Hormone Synthesis
There are six steps in the synthesis of thyroid hormone-
• Active transport of Iodide into the follicular cell via
Sodium-Iodide Symporter (NIS). This is actually secondary
active transport, and the sodium gradient driving it is
maintained by a Sodium-Potassium ATPase.
• Thyroglobulin (Tg), a large protein rich in Tyrosine, is
formed in follicular ribosomes and placed into secretory
vesicles.
• Exocytosis of Thyroglobulin into follicle lumen, where it is
stored as colloid. Thyroglobulin is the scaffold upon which
thyroid hormone is synthesised.
48JCR - Endocrine System
• Iodination of the Thyroglobulin. Iodide is made reactive by
the enzyme thyroid peroxidase. Iodide binds to the benzene
ring on Tyrosine residues of Thyroglobulin. First formed is
monoiodotyrosine (MIT) then diiodotyrosine (DIT).
• Coupling of MIT and DIT to give Triiodothyronine (T3)
hormone and coupling of DIT and DIT to give
Tetraiodothyronine (T4) hormone, also known as
Thyroxine.
• Endocytosis of iodinated thyroglobulin back into the
follicular cell. Thyroglobulin undergoes proteolysis in
lysosomes to cleave the iodinated tyrosine residues from the
larger protein. Free T3 or T4 is then released, and the
Thyroglobulin scaffold is recycled.
49JCR - Endocrine System
 Secretion of thyroid hormone-
• Thyroid hormones are released as part of a hypothalamic-
pituitary-thyroid axis. The Hypothalamus detects a low
plasma concentration of thyroid hormone and releases
Thyrotropin-Releasing Hormone (TRH) into the
hypophyseal portal system.
• TRH binds to receptors found on thyrotrophic cells of the
anterior pituitary gland, causing them to release Thyroid
Stimulating Hormone (TSH) into the systemic circulation.
TSH binds to TSH receptors on the basolateral membrane of
thyroid follicular cells and induces the synthesis and release
of thyroid hormone.
50JCR - Endocrine System
 Function
The thyroid gland is one of the main regulators of metabolism.
T3 and T4 typically act via nuclear receptors in target tissues
and initiate a variety of metabolic pathways. High levels of
them typically cause these processes to occur faster or more
frequently.
Metabolic processes increased by thyroid hormones include:
• Basal Metabolic Rate
• Gluconeogenesis
• Glycogenolysis
• Protein synthesis
• Lipogenesis
• Thermogenesis
51JCR - Endocrine System
 Thyroid Conditions-
• Goiter: A general term for thyroid swelling. Goiters can be
harmless, or can represent iodine deficiency or a condition
associated with thyroid inflammation called Hashimoto’s
thyroiditis.
• Thyroiditis: Inflammation of the thyroid, usually from a
viral infection or autoimmune condition. Thyroiditis can be
painful, or have no symptoms at all.
• Hyperthyroidism: Excessive thyroid hormone production.
Hyperthyroidism is most often caused by Graves disease or
an overactive thyroid nodule.
• Hypothyroidism: Low production of thyroid hormone.
Thyroid damage caused by autoimmune disease is the most
common cause of hypothyroidism . 52JCR - Endocrine System
• Graves disease: An autoimmune condition in which the
thyroid is overstimulated, causing hyperthyroidism.
• Thyroid cancer: An uncommon form of cancer, thyroid
cancer is usually curable. Surgery, radiation, and hormone
treatments may be used to treat thyroid cancer.
• Thyroid nodule: A small abnormal mass or lump in the
thyroid gland. Thyroid nodules are extremely common. Few
are cancerous. They may secrete excess hormones, causing
hyperthyroidism, or cause no problems.
• Thyroid storm: A rare form of hyperthyroidism in which
extremely high thyroid hormone levels cause severe illness
53JCR - Endocrine System
 Thyroid function tests-
• Thyroid function tests are a series of blood tests
used to measure how well your thyroid gland is
working. Available tests include the T3, T3RU, T4,
and TSH.
54JCR - Endocrine System
 T4 & TSH results-
• The T4 test and the TSH test are the two most common
thyroid function tests. They’re usually ordered together.
• The T4 test is known as the thyroxine test. A high level of
T4 indicates an overactive thyroid (hyperthyroidism).
Symptoms include anxiety, unplanned weight loss, tremors,
and diarrhea. Most of the T4 in your body is bound to
protein. A small portion of T4 is not and this is called free
T4. Free T4 is the form that is readily available for your
body to use. Sometimes a free T4 level is also checked
along with the T4 test.
• The TSH test measures the level of thyroid-stimulating
hormone in your blood. The TSH has a normal test range
between 0.4 and 4.0 milli-international units of hormone per
liter of blood (mIU/L). 55JCR - Endocrine System
 T3 result-
• The T3 test checks for levels of the hormone
triiodothyronine. It’s usually ordered if T4 tests and TSH
tests suggest hyperthyroidism. The T3 test may also be
ordered if you’re showing signs of an overactive thyroid
gland and your T4 and TSH aren’t elevated.
• The normal range for the T3 is 100–200 nanograms of
hormone per deciliter of blood (ng/dL). Abnormally high
levels most commonly indicate a condition called Grave’s
disease. This is an autoimmune disorder associated with
hyperthyroidism.
56JCR - Endocrine System
 Parathyroid Gland
57JCR - Endocrine System
 Structure
• 4 tiny parathyroid glands, in the neck, on the posterior
surface
of the thyroid gland. Have 2 superiorly & 2 inferiorly.
• Small in size, measuring about 6 mm long,
3 mm wide and 2 mm thick with dark brown color
58JCR - Endocrine System
59JCR - Endocrine System
 Histology
• Made up of chief cells & oxyphil cells
Chief cells
• Secrete parathormone
Oxyphil cells
• Degenerated chief cells and their function is
unknown.
• May secrete parathormone during physiological
condition called parathyroid adenoma.
60JCR - Endocrine System
 Parathormone
• Secreted by the chief cells of the parathyroid glands.
• Essential for the maintenance of blood calcium
level within a very narrow critical level.
• Maintenance of blood calcium level is necessary
because calcium is an inorganic ion for many
physiological functions.
61JCR - Endocrine System
Chemistry
• Parathormone is protein in nature, having 84 amino acids.
• It’s Molecular weight in 9,500.
Half life & Plasma level
• Parathormone has a half-life of 10 minutes.
• Normal plasma level of PTH is about 1.5-5.5 mg/dL.
62JCR - Endocrine System
 Actions of PTH on Blood Calcium Level
• Primary action of the PTH is to maintain the blood calcium
level within the critical range of 9-11 mg/dL
• PTH control blood calcium level by
1. Reabsorption of Ca from Bones
2. Reabsorption of Ca from renal tubules (Kidney)
3. Absorption of Ca from Gastrointestinal tract
63JCR - Endocrine System
On bones
• PTH enhances the reabsorption of Ca from the bones by
acting on osteoblasts and osteoclasts of the bone.
• Increases the number and activity of osteoclasts (bone
destroying cells).
• Increases collagen synthesis.
• Increases alkaline phosphatase activity.
• Increases local growth factors: IGF and transforming
factors.
64JCR - Endocrine System
On Kidney
• PTH increases the reabsorption of Ca from the renal tubules
along with magnesium ions and hydrogen ions Increases
Ca reabsorption mainly from distal convoluted tubule
and proximal part of collecting duct.
• PTH also increases the formation of 1, 25-di-
hydroxycholecalciferol (activated form of vitamin D) from
25-hydroxycholecalciferol in kidneys.
• Decreased phosphate, sodium and bicarbonate reabsorption
from the proximal tubule.
65JCR - Endocrine System
On Gastrointestinal Tract
• PTH increases the absorption of Ca ions from the GI tract
indirectly.
• The activated vitamin D is very essential for the absorption
of Ca from the GI tract.
• PTH also increase the absorption of PO4 & mg.
66JCR - Endocrine System
 Disorders of
Parathyroid Gland
67JCR - Endocrine System
 Tetany
Manifested by neuromuscular excitability due to plasma
ionized Ca2+
Causes:
a)Hypoparathyroidism
b)Alkalemia :Decrease the solubility product of Ca2+& PO4
and leads to reduced ionized Ca2+ & precipitation of CaPO4
c)Decreased Ca2+ absorption from the intestine:
1.Low calcium intake and Excess intake of antacids (peptic
ulcer) lead to Ca2+ precipitation and decreased absorption.
68JCR - Endocrine System
 Manifestation of Tetany
• These depend on the degree of red blood Ca2+ level:
1. Manifest tetany:
– Blood Ca2+ level is below 7 mg% (N 9-11 mg%).
– Muscular spasms in the hands and feet (Carpo-pedal
spasm).
2. Latent tetany:
– Blood Ca2+ level is at 7-9 mg%. 69JCR - Endocrine System
 Treatment of Tetany
1.IV injection of Ca2+ gluconate during spasm. Stops
immediately the tetanic spasms.
2. Calcium level is then maintained by giving vitamin D and
administration of oral calcium.
3.Acidifying salts as ammonium chloride help Ca2+ absorption
as they increase the ionization of Ca2+.
70JCR - Endocrine System
 Islets of Langerhans
of
Pancreas
71JCR - Endocrine System
 Pancreas
• A triangular gland, which has both exocrine and endocrine
cells, located behind the stomach
• Strategic location
• Acinar cells produce an enzyme-rich juice used for
digestion (exocrine product)
• Pancreatic islets (islets of Langerhans) produce hormones
involved in regulating fuel storage and use.
72JCR - Endocrine System
73JCR - Endocrine System
 Islets of Langerhans
• 1 Million islets
• 1-2% of the pancreatic mass
• Beta (β) cells produce insulin
• Alpha (α) cells produce glucagon
• Delta (δ) cells produce somatostatin
• F cells produce pancreatic polypeptide
74JCR - Endocrine System
75JCR - Endocrine System
 Insulin
• Hormone of nutrient abundance
• A protein hormone consisting of two amino acid chains
linked by disulfide bonds
• Synthesized as part of proinsulin (86 AA) and then excised
by enzymes, releasing functional insulin (51 AA) and C
peptide (29 AA).
76JCR - Endocrine System
 Insulin Structure
1- Large polypeptide 51 AA (MW 6000)
2- Tow chains linked by disulfide bonds.
A chain (21 AA)
B chain (30 AA)
3- Disulfide bonds.
77JCR - Endocrine System
78JCR - Endocrine System
 Insulin Action on Cells
• Insulin is the hormone of abundance.
• The major targets for insulin are:
– liver
– Skeletal muscle
– adipose tissue
• The net result is fuel storage
79JCR - Endocrine System
 Insulin Action on Carbohydrate
Metabolism
Liver:
• Stimulates glucose oxidation
• Promotes glucose storage as glycogen
• Inhibits glycogenolysis
• Inhibits gluconeogenesis
Muscle:
• Stimulates glucose uptake (GLUT4)
• Promotes glucose storage as glycogen
80JCR - Endocrine System
 Glucagon
• A 29-amino-acid polypeptide hormone that is a potent
hyperglycemic agent
• Produced by α cells in the pancreas
• Its major target is the liver, where it promotes:
– Glycogenolysis – the breakdown of glycogen to
glucose
– Gluconeogenesis – synthesis of glucose from lactic
acid and noncarbohydrates
– Release of glucose to the blood from liver cells
81JCR - Endocrine System
 Physiological Action of Glucagon
• Stimulates glycogenolysis, gluconeogenesis &
inhabits glycogenesis
• Promotes lipolysis & ketogenesis
• Increases calorigenesis
82JCR - Endocrine System
 Somatostatin
• Secreted from D cells of pancreas
• Also secreted from hypothalamus & GIT
• A peptide hormones with 2 forms, one with
14 AAs & the other with 28 Aas
Functions
➤ Inhibits secretion of insulin & glucagon
➤ Inhibits GI motility & GI secretions
➤ Regulates feedback control of gastric emptying
83JCR - Endocrine System
 Diabetes Mellitus (DM)
• A serious disorder of carbohydrate metabolism
• Results from hyposecretion or hypoactivity of insulin
• The three cardinal signs of DM are:
– Polyuria – huge urine output
– Polydipsia – excessive thirst
– Polyphagia – excessive hunger and food consumption
84JCR - Endocrine System
 Diabetes Mellitus Type l
Type 1: beta cells destroyed- no insulin produced chronic
fasted state, "melting flesh", ketosis, acidosis,
glucosuria, diuresis & coma
Diabetes Mellitus Type ll
• Over 15 million diabetics in USA- 10% type I, 90% type II
• More common is some ethnic groups
• Insulin resistance keeps blood glucose too high
• Chronic complications: atherosclerosis, renal failure&
blindness
85JCR - Endocrine System
86JCR - Endocrine System
 Symptoms of Diabetes Mellitus
➤ Hyperglycemia
➤ Polyuria
➤ Polydipsia
➤ Polyphagia
➤ Ketoacidosis
➤ Hyperlipidemia
➤ Muscle wasting
➤ Electrolyte depletion
87JCR - Endocrine System
 Diagnosis
• Demonstrating persistence hyperglycemia & glycosuria
• Glucose Tolerance Test (GTT) – oral is preferred
• Estimation of Fasting Blood Glucose (FBG)
• FBS more than 126 mg% in more than
two occasions confirms DM
Treatment
• Insulin therapy
• Oral hypoglycemic agents
• Life style modifications
88JCR - Endocrine System
Adrenal Glands
89JCR - Endocrine System
90JCR - Endocrine System
Our body has two adrenal (suprarenal) glands, each located
on the superior pole of each kidney. Each adrenal gland is
Structurally and functionally differentiated into two regions
or zones:
1.Adrenal Cortex
2. Adrenal medulla
91JCR - Endocrine System
 Adrenal Cortex
This is the outer or peripheral zone of the adrenal
gland, which makes up the bulk of the gland.
The adrenal cortex is divided into three zones. Each
zone has a different cellular arrangements and secrets
different groups of steroid hormones.
92JCR - Endocrine System
 Layers of Adrenal Cortex
1. Zona-glomerulosa
2. Zona-fasciculata
3. Zona-reticulata
Zona-glomerulosa:
• This is the outermost layer of the adrenal cortex
which secrets mineralocorticoid hormones.
• Immediately beneath the capsule.
• Columnar or pyramidal cells
• Arranged in closely packed, rounded, arched cords or
small clumps.
• Occupy 15% of the adrenal cortex. 93JCR - Endocrine System
 Zona-fasciculata
:
• This is the middle zone of the adrenal cortex which
secrets glucocorticoids hormone.
• Occupy 65% of the adrenal cortex.
• Polyhedral, often binucleated cells with lipid droplets in
their cytoplasm.
• Cells are also called spongyocytes due to vacuolization.
94JCR - Endocrine System
 Zona-reticularis
• This is the innermost layer of the adrenal cortex
which secrets androgen but in small quantities.
• Occupy 7% of the adrenal cortex.
• Smaller cells disposed in irregular cords forming
anastomosing network.
• Presence of lipofuscin pigment granules –large and
numerous.
95JCR - Endocrine System
 Hormones of the Adrenal cortex
The adrenocortical hormones and their functions in the body
are classified into three groups:
1. Mineralocorticoids
2. Glucocorticoids
3. Adrenal androgens.
Biosynthesis of adrenal hormones:
96JCR - Endocrine System
97JCR - Endocrine System
 Mineralocorticoids
Mineralocorticoids:
– secreted from the adrenal cortex-zona glomerulosa.
– Main secreted hormone is aldosterone.
– It also secrets deoxy-corticosterone,9-alpha
flourocortisol, cortisol, cortisone.
Functions:
– Maintain balance of electrolytes content of the body
fluid.
– Increased tubular reabsorption of Na+ ions in the
exchange for K+ and H+ ions.
98JCR - Endocrine System
 Mineralocorticoids
– Act mainly on the distal kidney tubules, salivary glands
and sweat glands.
– Increase blood volume and cardiac output.
– Increase blood pressure.
Regulations of aldosterone secretion :
– Increased of K+ ions.
– Decreased of Na+ ions.
– Undefined pituitary factors.
– ACTH
– Hypotension
– Increased renin angiotensin 99JCR - Endocrine System
 Glucocorticoids
Secreted from adrenal cortex-zona fasciculata.
Main secreted hormones are:
• Cortisol
• Prednisone & methyl
prednisone
• Corticosterone
• Cortisone
100JCR - Endocrine System
 Functions
Effects in the metabolism of carbohydrates, proteins and
lipids.
• Stimulation of gluconeogenesis.
• Mobilization of amino acids from extra
hepatic tissues.
• Inhibition of glucose uptake in muscles
and adipose tissues.
• Stimulation of fat breakdown. .
101JCR - Endocrine System
 Functions
• Suppress immune response.
• Destroying circulating
lymphocytes.
• Inhibiting mitotic activity.
• Controlling secretion of
cytokines.
– Promotes maturation of lungs and production of
surfactants in fetal development
102JCR - Endocrine System
 Androgen
• Secreted from the adrenal cortex-zona reticularis.
• Exhibit actions similar to testosterone.
Functions :
• Responsible for the development and maintenance of
reproductive functions.
• Stimulation of secondary sex characteristic.
• Stimulates the production of skeletal muscles and bones
and RBC.
103JCR - Endocrine System
104
• Regulations of androgen:
1. Controlled by luteinizing hormone (LH) and follicle
stimulating hormone(FHS).
2. Prolactin shows an inhibitory effects on androgen
secretion.
• Adrenal glands disorders :
1. Tumors including pheochromocytomas. Infections
2. Genetic mutations.
3. Cushing's syndrome.
4. Addison’s disease.
5. A problem in another gland, such as pituitary.
6. Hyperaldosteronism.
JCR - Endocrine System
 Adrenal Medulla
• Structure
• Biosynthesis of hormones
• Functions and regulations
• Disorder of adrenal medulla
105JCR - Endocrine System
Introduction
• The adrenal medulla is part of the adrenal gland it is
located at the center of the gland. It is surrounded by
adrenal cortex. It is the innermost part of the adrenal gland
and it has such type of cells that secrete epinephrine also
known as adrenaline and norepinephrine which is known
as noradrenaline. It also secretes dopamine at a small
amount in response to stimulation by sympathetic
preganglionic neurons.
• In general adrenal medulla is a less common site of
chemically induced degenerative lesions.
106JCR - Endocrine System
Structure of adrenal medulla
• The adrenal medulla consists of irregularly shaped cells
grouped around blood vessels. These cells are intimately
connected with the sympathetic division of the autonomic
nervous system(ANS).
• The cells of the adrenal medulla are derived from the neural
crest in contrast to the mesodermal origin of the adrenal
cortex. The secretory cells of the adrenal medulla are called
chromaffin cells because of the formation of colored
polymers of catecholamines after exposure to oxidizing
agents such as chromate.
• In fact these adrenal medullary cells are modified
postganglionic neurons and preganglionic autonomic nerve
fibers lead to them directly from the central nervous system.107JCR - Endocrine System
Structure of adrenal medulla
108JCR - Endocrine System
Functions of adrenal medulla
• Biosynthesis of hormones:
The adrenal medulla is the principal site of the conversion
of the amino acid tyrosine into the catecholamines
epinephrine, norepinephrine and dopamine.
• Stimulation of the sympathetic nerves to the adrenal
medullae causes large quantities of epinephrine and
norepinephrine to be released into the circulating blood,
and these two hormones in turn are carried in the blood to
all tissues of the body. On average, about 80 percent of the
secretion is epinephrine and 20 percent is
norepinephrine.
109JCR - Endocrine System
Functions of adrenal medulla
• The circulating epinephrine and norepinephrine have almost
the same effects on the different organs as the effects
caused by direct sympathetic stimulation, except that the
effects last 5 to 10 times as long because both of these
hormones are removed from the blood slowly over a period
of 2 to 4 minutes.
• The circulating norepinephrine causes constriction of most
of the blood vessels of the body; it also causes increased
activity of the heart, inhibition of the gastrointestinal
tract, dilation of the pupils of the eyes, and so forth.
110JCR - Endocrine System
111JCR - Endocrine System
Regulatory activity of adrenal
medulla
• Adrenal medulla is the part of the sympathetic system and
is important for the regulation of blood pressure .
Catecholamines released from the adrenal medulla also
have metabolic effects . The following are the most
important effects of catecholamines:
• They increase blood pressure , skeletal muscle blood flow,
skeletal contractility, heart rate, blood glucose, lipolysis.
• They decrease visceral blood flow ,gastrointestinal
contractility ,urinary output.
112JCR - Endocrine System
Disorder of the adrenal medulla
• Pathology within the adrenal medulla and the autonomic
nervous system is primarily because of neoplasms. The
most common tumour, called pheochromocytoma when
located in the adrenal medulla, originates from chromaffin
cells and excretes catecholamines.
• Those tumours found in extra-adrenal chromaffin cells are
sometimes referred to as secreting paragangliomas.
Neoplasms may also be of neuronal lineage, such as
neuroblastomas and ganglioneuromas.
113JCR - Endocrine System
Pheochromocytoma
• Pheochromocytoma is a chromaffin cell neoplasm that
typically causes symptoms and signs from episodic
catecholamine release, including paroxysmal
hypertension.
• In population-based cancer studies, its frequency is
approximately two cases per million of the population. The
diagnosis of pheochromocytoma is typically made in the
fourth or fifth decade of life without gender differences.
114JCR - Endocrine System
115JCR - Endocrine System
Paragangliomas
• Extra-adrenal pheochromocytomas can be referred to as
paragangliomas. They arise from paraganglionic
chromaffin cells in association with sympathetic nerves,
and are found in the organ of Zuckerkandl, urinary bladder,
chest, neck and at the base of the skull.
• They are more common in children than in adults, and are
more frequently malignant. As discussed earlier, mutations
in the SDH family may predispose to head and neck
paragangliomas and pheochromocytoma.
116JCR - Endocrine System
Paragangliomas
117JCR - Endocrine System
Neuroblastomas
• Neuroblastomas and ganglioneuromas are tumours of the
primitive neuroblast cells from the sympathetic nervous
system in ganglia and the adrenal medulla. They may
represent a continuum of neuronal maturation and are the
most common malignancy found in children, representing
7–10% of all childhood cancers.
• Because of their more mature ganglion cells which are
histologically benign, ganglioneuromas are often
metabolically inactive and asymptomatic. They are found
incidentally or with compressive symptoms mostly in the
posterior mediastinum or retroperitoneum.
118JCR - Endocrine System
Neuroblastoma
119JCR - Endocrine System
Nervous System 1
Nervous System
• Nervous system is the most important organization which control and
integrates the different body functions and maintains the constancy
of internal environment.
• A network of billions of nerve cells linked together in a highly
organized fashion to form the rapid control center of the body.
• Primarily, the nervous system is divided into two parts:
(1) Central nervous system (2) Peripheral nervous system
JCR/Human Physiology
Nervous System 2
Division of nervous system
JCR/Human Physiology
Nervous System 3
Division of nervous system
JCR/Human Physiology
Nervous System 4
Neuron
• Defined as the structural and functional unit of the nervous system
• It is otherwise called nerve cell.
• Neuron is different from other cells by two ways:
(i) neuron has branches or process called axon and dendrites
(ii) neuron does not have centrosome so it cannot undergo division
JCR/Human Physiology
Nervous System 5
Neuron: structure
The neuron is made up of three parts:
(1) Nerve cell body or soma
(2) Dendrites
(3) Axon
JCR/Human Physiology
JCR/Human Physiology Nervous System 6
Neuron: structure
Nerve cell body
• The nerve cell body is irregular in shape and is constituted by a mass of
cytoplasm called neuroplasm.
• The cytoplasm contains a large nucleus, nissl bodies, neurofibrils,
mitochondria and golgi apparatus.
• The nucleus does not contain centrosome, so they cannot multiply like other
cells.
• Nissl bodies are present in the soma but not in axon.
• Presence of neurofibrils is a characteristic feature of the neurons.
Neurofibrils are thread like structures present in the soma.
JCR/Human Physiology Nervous System 7
Neuron: structure
Dendrites
• It is the branched process of the
neuron and it is branched repeatedly.
• It is conductive in nature.
• It transmits impulses towards the
nerve cell body.
• Usually dendrites are shorter than
axon.
• Number varies from nil to numerous.
JCR/Human Physiology Nervous System 8
Neuron: structure
Axon
• It is the longer process of the nerve cell.
• Arises from axon hillock of the nerve cell
body.
• Devoid of Nissl granules.
• Extends for a long distance away from the
nerve cell body.
• The length of the longest axon is about one
meter.
JCR/Human Physiology Nervous System 9
Neuron: Myelin sheath
• In a myelinated nerve fiber, the axis cylinder is
covered by a thick tubular sheath called myelin
sheath.
• Does not form a continuous sheath and is absent at
regular interval.
• The area where the myelin sheath is absent is called
node of Ranvier.
• Myelin sheath is responsible for the white color of
the nerve fibers.
JCR/Human Physiology Nervous System 10
Myelin sheath: Functions
1. Myelin sheath is responsible for faster
conduction of impulse through the nerve
fibers.
2. Myelin sheath has a high insulating capacity.
Because of this quality, the myelin sheath
restricts the nerve impulse within the single
nerve fiber, and prevents the stimulation of
neighboring nerve fibers.
JCR/Human Physiology Nervous System 11
Myelinogenesis
• Myelin sheath is formed from wrapping of Schwann cell around the axis
cylinder in many concentric layers.
• The process of the formation of myelin sheath is called the myelinogenesis.
• In the peripheral nerve, the myelinogenesis starts at 4th month of
intrauterine life. It is completed only in the second year after birth.
• The axon is first enveloped completely by Schwann cell membrane.
• The Schwann cell membrane then gives several turns leaving the axon
surrounded by many concentric layers.
JCR/Human Physiology Nervous System 12
Myelinogenesis
JCR/Human Physiology Nervous System 13
Myelinogenesis
• During this repeated wrapping, more and more cytoplasm is pushed to the
periphery of the Schwann cell.
• When the myelination process is completed, the Schwann cell covers the
axon with many layers of plasma membranes. This covering is called a myelin
sheath.
• The Schwann cell cytoplasm outside the myelin sheath contains the cell
nucleus and referred to as the neurolema.
JCR/Human Physiology Nervous System 14
Classification of Neurons
A. Based on the number of processes that emanate from their cell body, neurons can be
classified as:
1. Apolar (have no process)
• Apolar neurons are type of neuron which contain only one protoplasmic process extends from
cell body.
• Such neurons are common in insects.
• Apolar neurons are specific to the cerebellum and granule region of the dorsal cochlear nucleus.
2. Unipolar (only axon, i.e., 5th cranial nerve)
• A unipolar neurons is a type of neuron in which only one protoplasmic process (neurite) extends
from the cell body.
• Most neurons are multipolar, generating several dendrites and an axon and there are also
many bipolar neurons.
• Unipolar neurons that begin as bipolar neurons during development are known
as pseudounipolar neurons.
• Typically these have special structures for transducing some type of physical stimulus (light,
sound, temperature, etc.) into electrical activity, no dendrites, and a single axon that conveys the
resulting signals into the spinal cord or brain.
3. Bipolar (both axon and dendrite, i.e., retina)
• A bipolar neurone or bipolar cell, is a type of neuron which has two extensions (one axon and
one dendrite).
• Bipolar cells are specialized sensory neurons for the transmission of special senses.
• As such, they are part of the sensory pathways
for smell, sight, taste, hearing and vestibular functions.
4. Pseudounipolar
• cell body in one side, T-shaped, one branch of T being the dendrite and another branch is
axon, found in all spinal ganglia.
• A pseudounipolar neuron (pseudo – false, uni – one) is a kind of sensory neuron in the
peripheral nervous system.
5. Multipolar
• A multipolar neuron is a type of neuron that possesses a single axon and many dendrites,
allowing for the integration of a great deal of information from other neurons.
• These processes are projections from the nerve cell body.
• Multipolar neurons constitute the majority of neurons in the central nervous system.
• They include motor neurons and interneurons are most commonly found in the cortex of
the brain, the spinal cord, and also in the autonomic ganglia.
JCR/Human Physiology Nervous System 15
JCR/Human Physiology Nervous System 16
JCR/Human Physiology Nervous System 17
Classification of Neurons
B. According to function:
1. Sensory Neuron (Afferent):
convey information from tissues and organs into the central nervous system.
2. Motor Neuron (Efferent):
transmit signals from the central nervous system to the effector cells/tissue.
3. Interneurons:
connect neurons within specific regions of the central nervous system.
JCR/Human Physiology Nervous System 18
Nerve fibers
• A nerve fiber is a threadlike extension of a
nerve cell and consists of an axon
(microfilament + microtubule) and myelin
sheath (if present) in the nervous system.
JCR/Human Physiology Nervous System 19
Classification of nerve fiber
Nerve fibers are classified by six methods:
(1) Depending upon structure
(2) Depending upon distribution
(3) Depending upon origin
(4) Depending upon function
(5) Depending upon the secretion of neurotrnsmittter
(6) Depending upon diameter and conduction
JCR/Human Physiology Nervous System 20
Classification of nerve fibers
(1) Based on the structure, the nerve fibers
are classified into two ways:
1. Myelinated nerve fibers: covered by
myelin sheath
2. Non-myelinated nerve fibers: do not
have myelin sheath.
JCR/Human Physiology Nervous System 21
Classification of nerve fibers
(2) Based on distribution, the nerve fibers are classified into two ways:
1. Somatic nerve fibers: supply the skeletal muscle of the body.
2. Autonomic or Visceral nerve fibers: supply the various internal organs of
the body.
(3) Based on origin, the nerve fibers are classified into two ways:
1. Cranial nerve fibers: arising from the brain.
2. Spinal nerve fibers: arising from the spinal cord.
JCR/Human Physiology Nervous System 22
Classification of nerve fibers
(4) Based on function, the nerve fibers are classified into two ways:
1. Motor or Efferent nerve fibers: carry motor impulses from CNS to PNS.
2. Sensory or Afferent nerve fibers: carry sensory impulses from PNS to
CNS.
(5) Based on secretion of neurotransmitter, the nerve fibers are classified into
two ways:
1. Adrenergic nerve fibers: secrete noradrenaline or norepinephrine.
2. Cholinergic nerve fibers: secrete achetylcholine.
JCR/Human Physiology Nervous System 23
Classification of nerve fibers
(6) Based on diameter and conduction, the nerve fibers are classified into three
major types:
1. Type A nerve fibers: further classified into (i) Type A alpha (ii) Type A beta
(iii) Type A gamma and (iv) Type B delta
2. Type B nerve fibers
3. Type C nerve fibers
• The diameter (thickness) of the nerve fibers: Type A alpha (12 to 24 μ)>
Type A beta> Type A gamma > Type A delta> Type B> Type C (<1.5 μ)
• The velocity of conductance of the nerve fibers: Type A alpha (70 to 120
m/s)> Type A beta> Type A gamma > Type A delta> Type B> Type C (0.5 to 2
m/s)
JCR/Human Physiology Nervous System 24
Properties of nerve fibers
(1) Excitability: The nerve can be stimulated or excited by a suitable
stimulus, which may be:
-mechanical
-thermal
-chemical
-electrical
The stimulus must be adequate to produce the action potential, which is
propagated.
• Excitability depends upon the following factors:
(a) Strength of stimulus
(b) Duration of stimulus
(c) Frequency of stimulus
(d) Injury
JCR/Human Physiology Nervous System 25
Properties of nerve fibers
(2) Conductivity: Conductivity of nerve fiber shows the following
characteristics:
(i) Impulse is propagated along a nerve in both directions [but under
normal conditions the nerve impulse travels in one direction only-in the
motor nerve towards the responding organ; in sensory nerve toward the
center]
(ii) The nerve impulse is propagated with a definite speed. The conduction
velocity depends upon the diameter of the nerve fibers, the thicker
fibers showing higher velocity. The velocity also depends on the
myelination and on temperature.
JCR/Human Physiology Nervous System 26
Properties of nerve fibers
3. All-or-none law:
-When a nerve is stimulated by a stimulus with sub-threshold strength,
action potential does not develop. If the strength of stimulus is above the
sub-threshold level, action potential will develop and response will take
place.
-If the strength or duration of the stimulus be further increased, no
alteration in the response will take place. The action potential remains the
same.
4. Refractory period:
When the nerve fiber is once excited, it will not respond to a second
stimulus for a brief period. This period is called refractory period.
JCR/Human Physiology Nervous System 27
Properties of nerve fibers
5. Summation:
When one subliminal stimulus is applied, it does not produce any response
in the nerve fiber. However, if two or more subliminal stimuli are applied
within a short interval, the response is produced. It is because the subliminal
stimuli are summed up together.
6. Adaptation:
While stimulating a nerve fiber continuously, the excitability of the nerve
fiber is maximum in the beginning. Later the response decreases slowly and
finally the nerve fiber does not show any response at all. This phenomenon is
known as adaptation.
JCR/Human Physiology Nervous System 28
Properties of nerve fibers
7. Accommodation:
If a stimulus even in stronger strength is applied very slowly to a nerve,
then there may have no response only due to lack of attaining the
threshold strength. This phenomenon is called accommodation.
8. Indefatigability:
A nerve fiber cannot be fatigued, even if it is stimulated continuously for a
long time. The reason for this is the nerve fiber can conduct only one
action potential at a time. At that time, it is completely refractory and does
not conduct another action potential.
JCR/Human Physiology Nervous System 29
Neuroglia
• Neuroglia or glia is the supporting cell of the nervous system.
• They are non excitable and do not transmit nerve impulse.
• Compared to the number of neurons, the number of glial cells is 10 to 15 times greater.
Classification:
(1) Central neuroglial cells
(a) Astrocytes
(b) Microglia
(c) Oligodendrocytes
(2) Peripheral neuroglial cells
(a) Schwann cell
(b) Satellite cell
JCR/Human Physiology Nervous System 30
Central neuroglial cells : Astrocytes
• Star shaped cells present in all parts of the
brain.
• Two types: (i) Fibrous astrocytes and (ii)
Protoplasmic astrocytes
• Fibrous Astrocytes:
• Occupy mainly the white matter.
• Processes of these cells cover the nerve cells
and synapses.
• Form the Blood Brain Barrier (BBB)
• Protoplasmic Astrocytes:
• Present mainly in gray matter.
JCR/Human Physiology Nervous System 31
Central neuroglial cells : Astrocytes
Functions of Astrocytes:
• Form supporting network in brain and spinal
cord.
• From BBB thereby regulate the entry of
substances from blood into brain tissues.
• Provide calcium and potassium and regulate
neurotransmitter level in synapse.
• Regulate recycling of neurotransmitter during
synaptic transmission.
JCR/Human Physiology Nervous System 32
Central neuroglial cells : Microglia
• Derived from monocytes
• Enter the tissues of nervous system
from blood
• Engulf and destroy the microorganisms
and cellular debris by phagocytosis
JCR/Human Physiology Nervous System 33
Central neuroglial cells : Oligodendrocytes
• Cells forming myelin sheath around the
nerve fibers in CNS.
• Provide support to the CNS by forming a
semi-stiff connective tissue between the
neurons.
JCR/Human Physiology Nervous System 34
Peripheral neuroglial cell: Schwann cell
• Major glial cells in PNS.
• Provide myelination around the nerve fibers in PNS.
• Play important role in nerve regeneration.
• Remove cellular debris by their phagocytic activity.
JCR/Human Physiology Nervous System 35
Peripheral neuroglial cell : Satellite cells
• Present in the exterior surface of PNS neurons.
• Provide physical support to the PNS neurons.
JCR/Human Physiology Nervous System 36
Action Potential
• When two electrodes are connected through a suitable
amplifier and placed on the surface of a single axon, no
potential difference is observed.
• However, if one electrode is inserted into the interior of the
cell, a constant potential difference is observed, with the
inside negative relative to the outside of the cell at rest.
• A membrane potential results from separation of positive and negative
charges across the cell membrane.
• In resting cell the surface is positively charged and the interior is
negatively charged.
• In neurons, the resting membrane potential is usually about –70 mV
JCR/Human Physiology Nervous System 37
JCR/Human Physiology Nervous System 38
Stages of Action Potential
Resting stage:
• This is the resting membrane potential before the action potential begins.
• The membrane is said to be “polarized” during this stage because of the –70
millivolts negative membrane potential that is present.
Depolarization stage:
• At this time, the membrane suddenly becomes very permeable to sodium ions,
allowing tremendous numbers of positively charged sodium ions to diffuse to the
interior of the axon.
• The normal polarized stage is immediately neutralized by the inflowing positively
charged sodium ions, with the potential rising rapidly in the positive direction. This is
called depolarization.
JCR/Human Physiology Nervous System 39
JCR/Human Physiology Nervous System 40
Stages of Action Potential
Repolarization Stage
• After depolarization stage when the sodium channels begin to close and the
potassium channels open more than normal.
• Then, rapid diffusion of potassium ions to the exterior re-establishes the
normal negative resting membrane potential. This is called repolarization of
the membrane.
• In the last part of repolarisation the rate of fall is being abruptly slowed. This
slower fall is known as negative after-potential.
JCR/Human Physiology Nervous System 41
Stages of Action Potential
Repolarization Stage
• After reaching the basal level the wave overshoots slightly but slowly in the
hyperpolarisation direction. This is known as positive after potential.
• The Absolute Refractory Period:
Just after the neuron has generated an action potential, it cannot generate another
one. Many sodium channels are inactive and will not open, no matter what voltage
is applied to the membrane. Most potassium channels are open. This period is
called the absolute refractory period.
The neuron cannot generate an action potential because sodium cannot move in
through inactive channels and because potassium continues to move out through
open voltage-gated channels. A neuron cannot generate an action potential during
the absolute refractory period.
JCR/Human Physiology Nervous System 42
Stages of Action Potential
• The Relative Refractory Period:
Immediately after the absolute refractory period, the cell can generate an action potential, but
only if it is depolarized to a value more positive than normal threshold. This is true because
some sodium channels are still inactive and some potassium channels are still open. This is
called the relative refractory period.
The cell has to be depolarized to a more positive membrane potential than normal threshold
to open enough sodium channels to begin the positive feedback loop. The lengths of the
absolute and relative refractory periods are important because they determine how fast
neurons can generate action potentials.
• Resting state:
Resting state is when membrane potential returns to the resting voltage that occurred before
the stimulus occurred
JCR/Human Physiology Nervous System 43
Propagation of action potential
• Conduction of nerve impulse through a myelinated nerve fiber is about 50
times faster than through a nonmyelinated fiber.
• This is because the action potential jumps from one node to another node of
Ranvier.
• This type of jumping of action potential from one node to another is called
SALTATORY CONDUCTION.
JCR/Human Physiology Nervous System 44
Conduction of nerve impulse
JCR/Human Physiology Nervous System 45
Propagation of action potential
• The myelin sheath is not permeable to ions. So, the entry of sodium from
extracellular fluid into nerve occurs only in the node of Ranvier, where the
myelin sheath is absent.
• It causes depolarization in the node, and not in the internode. Thus, the
depolarization occurs at seccessive nodes.
• So, the action potential jumps from one node to another. Hence, it is called
SALTATORY CONDUCTION.
JCR/Human Physiology Nervous System 46
Synapse
• The junction between the two neurons is called synapse.
• It is the physiological continuity between two nerve cells.
JCR/Human Physiology Nervous System 47
The synapse consists of:
a presynaptic ending that contains neurotransmitters,
mitochondria and other cell organelles,
a postsynaptic ending that contains receptor sites for
neurotransmitters and,
a synaptic cleft or space between the presynaptic and
postsynaptic endings. It is about 20nm wide.
JCR/Human Physiology Nervous System 48
JCR/Human Physiology Nervous System 49
Types of synapse
According to the nature of synapse formation:
(1) Electrical synapses
(2) Chemical synapses
According to the nature of connections:
(1) Axosomatic
(2) Axodendritic
(3) Axo-axonic
JCR/Human Physiology Nervous System
50
Electrical Synapses
• Pre- and postsynaptic neurons joined by gap junctions
• Allow local current to flow between adjacent cells.
• Rare in CNS or PNS
• Found in cardiac muscle and many types of smooth muscle.
JCR/Human Physiology Nervous System 51
Chemical synapse
• The transfer of information across the synapse are brought about by
chemical process.
• Neurotransmitter is released from presynaptic neuron which travels the
synaptic cleft and bind with the receptors on the postsynaptic neuron
which facilitates ion channels opening and produces action potentials.
JCR/Human Physiology Nervous System 52
Chemical Synapse
JCR/Human Physiology Nervous System 53
Types of synapse
• Axosomatic: The presynaptic terminal of the axon ends in the cell body
(soma) of the neuron.
JCR/Human Physiology Nervous System 54
Types of synapse
Axodendritic synapse
• The presynaptic fibers of any axon
end in the dendrites of the
postsynaptic cell.
Axo-axonic synapse
• The presynaptic axon form synapse
with the axon of post synaptic cells.
• Rare synapse.
JCR/Human Physiology Nervous System 55
Mechanism of synaptic transmission
1. Arrival of action potential on presynaptic neuron opens volage-
gated Ca++ channels.
2. Ca2+ influx into presynaptic terminal.
3. Ca2+ acts as intracellular messenger stimulating synaptic
vesicles to fuse with membrane and release Neurotransmitter
(NT) via exocytosis.
4. NT diffuses across synaptic cleft and binds to receptor on
postsynaptic membrane.
JCR/Human Physiology Nervous System 56
Mechanism of synaptic transmission
JCR/Human Physiology Nervous System 57
Mechanism of synaptic transmission
5. Receptor changes shape of ion channel opening it and changing
membrane potential.
6. Opening of all types of ion channels causes a localized
depolarization of the membrane and produces an excitatory
postsynaptic potential (EPSP).
7. Selective opening of only the smaller ions like K+ and Chloride ions,
causing hyperpolarization of the membrane and that constitutes the
inhibitory postsynaptic potential (IPSP).
JCR/Human Physiology Nervous System 58
Mechanism of synaptic transmission
9. If the EPSP exceeds threshold value, it initiates the propagated
action potential in the postsynaptic neuron or muscle action
potential (MAP) in most skeletal and cardiac muscle.
10. During the development of the EPSP, simultaneously IPSP may
be developed at the same site by incoming action potential from
other sources. The propagation of nerve impulse by EPSP is
dependent upon the intensity of the postsynaptic potential.
11. NT is quickly destroyed by enzymes or taken back up by
astrocytes or presynaptic membrane.
JCR/Human Physiology Nervous System 59
Properties of synapse
(1) Law of forward conduction/One way conduction:
• An impulse is allowed to pass through a synapse in one direction only, i.e., from
presynaptic neuron to postsynaptic neuron.
(2) Synaptic delay:
• During the transmission of impulse via synapse, there is a short delay in
transmission. It is called synaptic delay. Synaptic delay in chemical synapse is less
than 0.5 millisecond.
• The synaptic delay is due to:
• Release of neurotransmitter
• Movement of neurotransmitter from axon terminal to postsynaptic
membrane
• Action of neurotransmitter to open the ionic channels in postsynaptic
membrane
JCR/Human Physiology Nervous System 60
Properties of synapse
(3) Fatigue:
• The synaptic fatigue is due to exhaustion of transmitter materials from the synaptic
vesicles following repeated presynaptic stimulation at faster rate.
(4) Summation:
• If the stimulus be subminimal, the released neurotransmitter will produce EPSP
which will not be sufficient to produce discharge of impulse in the postsynaptic
neuron. But if a number of subminimal stimuli be applied, their effects will be
summated together and the EPSP will be sufficient to discharge a impulse.
• Summation is of two types:
• (a) Spatial summation: when many presynaptic terminals are stimulated simultaneously.
• (b) Temporal summation: when one presynaptic terminal is stimulated repeatedly.
JCR/Human Physiology Nervous System 61
Properties of synapse
(5) Inhibition:
(A) Postsynaptic inhibition:
• The postsynaptic inhibition is due to release of inhibitory NT.
• This inhibitory NT change of permeability of the membrane which cause
hyperpolarization of the postsynaptic membrane and consequently, the action
potential elicited by the excitatory stimulus will fail to occur.
(B) Presynaptic inhibition:
• Inhibition of a stimulatory neuron before it synapses, by inhibiting Ca2+ entry and
blocking downstream processes, preventing neurotransmitter release, and
therefore preventing the neuron generating and EPSP post-synaptically.
JCR/Human Physiology Nervous System 62
Properties of synapse
(6) Synaptic block:
• The inhibitory neurotransmitter may be blocked at the synaptic junction producing
convulsion.
• Strychnine (pesticide) blocks the inhibitory activity and causes reduction or abolition
of the IPSP in most of the synaptic junctions.
• Tetanus toxin also has got similar effects and produces convulsion by blocking the
inhibitory neurotransmitter.
JCR/Human Physiology Nervous System 63
Neurotransmitter
• Neurotransmitters are endogenous chemicals that act as the mediator for
the transmission of nerve impulse from one neuron to another neuron
through a synapse.
• Neurotransmitters are packaged into synaptic vesicles and are released into
the synaptic cleft, where they bind to receptors in the membrane on the
postsynaptic side of the synapse.
• Release of neurotransmitters usually follows arrival of an action potential
at the synapse.
JCR/Human Physiology Nervous System 64
Types of neurotransmitter
(1) According to the nature (chemistry) of NT
(a) Amino acids:
• NT of this group are involved fast synaptic transmission and are inhibitory and
excitatory in aciton
• Examples:
• γ-aminobutyric acid (GABA) [inhibitory]
• Glutamate (glutamic acid) [excitatory]
• Aspartate (aspartic acid) [excitatory]
• Glycine [inhibitory]
(b) Monoamines:
• NT of this group involve in slow synaptic transmission and may be inhibitory
and excitatory in action.
• Acetylcholine (excitatory and inhibitory)
• Serotonin (inhibitory)
JCR/Human Physiology Nervous System 65
Types of neurotransmitter
(1) According to the nature (chemistry) of NT
(c) Catecholamines:
• Dopamine (inhibitory)
• Epinephrine (Adrenaline) [excitatory & inhibitory]
• Norepinephrine (Noradrenaline) [excitatory & inhibitory]
(d) Others:
• Nitric oxide (excitatory)
• Histamine [excitatory]
JCR/Human Physiology Nervous System 66
Types of neurotransmitter
(2) Based on the activity on postsynaptic neuron
(a) Excitatory NT
• Responsible for the conduction of impulse from presynaptic neuron to the post
synaptic neuron.
• Causes depolarization in the postsynaptic neuron.
• Causes development of EPSP.
• Example:
• Acetylcholine
• Aspartate
• Histamine
• Glutamate
JCR/Human Physiology Nervous System 67
Types of neurotransmitter
(b) Inhibitory NT
• Inhibit the conduction of impulse from presynaptic neuron to the post synaptic
neuron.
• Causes hyperpolarization in the postsynaptic neuron.
• Causes development of IPSP
• Example:
• GABA
• Dopamine
• Serotonin
• Glycine
JCR/Human Physiology Nervous System 68
Transport and release of NT
• The NT is produced in the cell body of neuron and is transported through the axon.
• At the axon terminal, the NT is stored in small packets called vesicles.
• Under the influence of a stimulus, these vesicles open and release the NT into the synaptic cleft.
• It binds to specific receptors on the surface of the postsynaptic neuron.
• The receptors are G proteins, protein kinase or ligand gated receptors.
JCR/Human Physiology Nervous System 69
Inactivation of NT
• After the execution of the action, neurotransmitter is inactivated by following
mechanisms:
• (1) It diffuses out of synaptic cleft to the area where it has no action
• (2) It is destroyed or disintegrated by specific enzymes
• (3) It is engulfed and removed by astrocytes
• (4) It is removed by reuptake process, i.e. the neurotransmitter is taken
back into the axon terminal from where it was released.
Functions of Neurotransmitters
1. Acetylcholine:
This neurotransmitter was discovered in the year 1921, by Otto Loewi. It is
mainly responsible for stimulating muscles. It activates the motor neurons that
control the skeletal muscles. It is also concerned with regulating the activities
in certain areas of the brain, which are associated with attention, arousal,
learning, and memory. People with Alzheimer's disease are usually found to
have a substantially low level of acetylcholine.
2. Dopamine:
Dopamine is the neurotransmitter that controls voluntary movements of the
body, and is associated with the reward mechanism of the brain. In other
words, dopamine regulates the pleasurable emotions.
Drugs like cocaine, heroin, nicotine, opium, and even alcohol increase the level
of this neurotransmitter. A significantly low level of dopamine is associated
with Parkinson's disease, while the patients of schizophrenia are usually found
to have excess dopamine in the frontal lobes of their brain.
JCR/Human Physiology Nervous System 70
3. Serotonin:
Serotonin is an important inhibitory neurotransmitter, which can have a profound
effect on emotion, mood, and anxiety. It is involved in regulating sleep,
wakefulness, and eating. It plays a role in perception as well. The hallucinogenic
drugs like LSD actually bind to the serotonin receptor sites, and thereby block the
transmission of nerve impulses, in order to alter sensory experiences.
4. Gamma-aminobutyric Acid (GABA):
GABA is an inhibitory neurotransmitter that slows down the activities of the
neurons, in order to prevent them from getting over excited. When neurons get
over excited, it can lead to anxiety. GABA can thus help prevent anxiety.
GABA is a non-essential amino acid, that is produced by the body from glutamate.
A low level of GABA can have an association with anxiety disorders. Drugs like
Valium work by increasing the level of this neurotransmitter. Alcohol and
barbiturates can also influence GABA receptors.
JCR/Human Physiology Nervous System 71
5. Glutamate:
Glutamate is an excitatory neurotransmitter that was discovered in 1907 by
Kikunae Ikeda of Tokay Imperial University. It is the most commonly found
neurotransmitter in the central nervous system. Glutamate is mainly associated
with functions like learning and memory. An excess of glutamate is however, toxic
for the neurons. An excessive production of glutamate may be related to the
disease, known as amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease.
6. Epinephrine and Norepinephrine:
Epinephrine (also known as adrenaline) is an excitatory neurotransmitter, that
controls attention, arousal, cognition, and mental focus. Norepinephrine is also an
excitatory neurotransmitter, and it regulates mood and physical and mental
arousal. An increased secretion of norepinephrine raises the heart rate and blood
pressure.
JCR/Human Physiology Nervous System 72
7. Endorphins:
Endorphins are the neurotransmitters that resemble opioid compounds, like
opium, morphine, and heroin in structure. The effects of endorphins on the body
are also quite similar to the effects produced by the opioid compounds. In fact, the
name 'endorphin' is actually the short form for 'endogenous morphine'.
Like opioids, endorphins can reduce pain, stress, and promote calmness and
serenity. The opioid drugs produce similar effects by attaching themselves to the
endorphin receptor sites. Endorphins enable some animals to hibernate by slowing
down their rate of metabolism, respiration, and heart rate.
8. Melatonin:
It is the hormone produced by the pineal gland that also acts as a
neurotransmitter. It basically controls the sleep-wake cycle. It is also
associated with controlling mood and sexual behavior. The production
of melatonin is dependent on light. Light to the retina inhibits the
production of melatonin, while darkness has a stimulating effect on its
production.
JCR/Human Physiology Nervous System 73
• 9.
Nitric Oxide:
It is a gas that acts both as a hormone and neurotransmitter,
depending on the specific requirement. It can cause the blood vessels
to dilate, besides preventing the formation of clots. This in turn, can
promote the circulation of blood. Nitric oxide can increase the level of
oxygen in the body, and improve memory, learning, alertness, and
concentration. It is also responsible for causing the smooth
gastrointestinal muscles to relax.
To sum up, neurotransmitters are chemicals that allow the nerves to
communicate with each other, and thus, regulate the various
functions of the body. A substantially high or low level of these
chemicals can alter the functions of the entire nervous system.
JCR/Human Physiology Nervous System 74
 Reflex-
• A reflex action, also known as a reflex, is an
involuntary and nearly instantaneous
movement in response to a stimulus.
• When a person accidentally touches a hot
object, they automatically jerk their hand away
without thinking.
• A reflex does not require any thought input.
JCR/Human Physiology Nervous System 75
 Classification of reflexes-
Reflexes
Clinical
Classification
Superficial
Deep
Visceral
Pathological
Anatomic
Classification
Segmental
Intersegmental
Suprasegmental
No . of
Synapses
Asynaptic
Monosynaptic
Polysynaptic
Bisynaptic
Functional
Classification
Flexor
Extensor
Righting
Postural
Withdrawal
Conditioned
Unconditioned
JCR/Human Physiology Nervous System 76
 Clinical Classification-
• Superficial- stimulating superficial structures.
• Deep- stimulating receptors deep in muscle.
• Visceral- stimulating receptors in viscera.
• Pathological- present only during abnormality.
JCR/Human Physiology Nervous System 77
 Anatomic Classification-
• Segmental- reflex arc pass through one anatomic segment
Example- knee jerk
• Intersegmental- involve> one segment
Example- crossed extensor response
• Suprasegmental- involve interaction with suprasegmental
components
Example- postural reflexes (head-limb)
JCR/Human Physiology Nervous System 78
 Number of synapses-
• Asynaptic- axon reflex
• Monosynaptic- stretch reflex
• Bisynaptic- reciprocal innervation
• Polysynaptic- superficial reflex
JCR/Human Physiology Nervous System 79
 Functional Classification-
• Flexor reflexes
• Extensor reflexes
• Righting reflexes
• Postural reflexes
• Withdrawal reflexes
JCR/Human Physiology Nervous System 80
 Others-
• Unconditioned reflexes- inborn or inherent reflexes.
• Conditioned reflexes- acquired reflexes.
Secretion of saliva when food is kept in mouth is
unconditioned reflex.
secretion even with thought is conditioned reflex.
JCR/Human Physiology Nervous System 81
 Reflex arc
• The neural pathway that controls the reflexes occurs
through the reflex arc.
• It acts on an impulse even before it reaches the brain.
• There are some stimuli that require an automatic,
instantaneous response without the need of conscious
thought.
The following diagram shows the reflex arc pathway-
JCR/Human Physiology Nervous System 82
JCR/Human Physiology Nervous System 83
Reflex arc: composition
(1) Receptor:
It is the end organ, which receives the stimulus.
(2) Afferent nerve:
Afferent or sensory nerve transmits sensory impulses from the receptor to
the center.
Composition:
A simple reflex arc includes five components:
(1) Receptors
(2) Afferent/sensory nerve
(3) Center
(4) Efferent/motor nerve
(5) Effector ogran
JCR/Human Physiology Nervous System 84
Reflex arc: composition
(3) Center:
• The center is located in the brain or spinal cord.
• The center receives the sensory impulses via afferent nerve fibers and in
return, it generates appropriate motor impulses.
• Afferent and efferent are connected here by interneurons.
(4) Efferent nerve:
Efferent or motor nerve transmits motor impulses from the center to the effector
organ.
(5) Effector organ:
The effector organ such as the muscle or gland shows the response to the stimulus.
JCR/Human Physiology Nervous System 85
Types of reflex arc
(1) Monosynaptic reflex arc:
Has only two neurons, i.e, only one synapse.
JCR/Human Physiology Nervous System 86
Types of reflex arc
(2) Polysynaptic reflex arc:
Consists of several neurons and two or more synapses.
JCR/Human Physiology Nervous System 87
Types of reflex arc
(3) Complex or conditioned reflex arc:
• This type of reflex involves the brain.
• Salivation on smelling one's favorite food is
an example of conditional reflex. The
individual recognizes the smell and based on
a previous experience, the response
(salivation) occurs.
• The ringing of the bell is called the
conditioned stimulus. The dog had, thus,
'learnt' to associate the sound of the bell to
food and this made it salivate at the sound of
the bell.
JCR/Human Physiology Nervous System 88
Types of reflex arc
(4) Asynaptic reflex or Axon reflex arc:
• The reflex arc has neither an integration center nor
any synapse.
• Axon reflexes are important in a lot of physiological
and physiopathological processes from regulation
of skin blood flow and sweating to inflammation
and pain, from itch to asthma bronchiale and
allergic rhinitis.
• This is not a true reflex arc.
JCR/Human Physiology Nervous System 89
Properties of reflexes
(1) One way conduction:
• During any reflex activity, the impulses are transmitted in only one direction
through the reflex arc.
• The impulse pass from receptors to the center and then from center to effector
organ.
(2) Reaction time/ synaptic delay:
• There is a short interval between the application of stimulus and the onset of
reflex response.
• This time is lost in crossing the number of synapses in the central nervous
system.
JCR/Human Physiology Nervous System 90
Properties of reflexes
(3) Summation:
Both spatial summation and temporal summation play an important role in the
facilitation of response during the reflex activity.
(i) Spatial summation: when two afferent nerve fibers supplying a muscle are
stimulated separately with subminimal stimulus, there is no response. But, if both
the nerve fibers are stimulated together with same strength of stimulus, the muscle
contracts. It is called spatial summation.
(ii) Temporal summation: When one nerve fiber is stimulated repeatedly with
subminimal stimuli, these stimuli are summed up to give response in the muscle. It
is called temporal summation.
JCR/Human Physiology Nervous System 91
Properties of reflexes
(4) Occlusion:
• When a reflex contraction is produced by simultaneous stimulation of two afferent
nerves, the amount of tension (T) in the muscle is less that the sumtotal of the
tensions (t1+t2) setup in the same muscle when the two afferent nerves are
separately stimulated (i.e., T<t1+t2).
• Occlusion is due to the overlapping of the nerve fibers during the distribution.
(5) Facilitation:
• The passage of a reflex impulse facilitates the transmission of the next impulse (by
reducing synaptic resistance).
• Each subsequent stimulus seems to exert a better effect than the previous one and
makes the passage of the next impulse easier.
JCR/Human Physiology Nervous System 92
Properties of reflexes
(6) Fatigue:
• When a reflex activity is continuously elicited for a long time, the response is
reduced slowly and at one stage, the response does not occur. This type of failure to
give response to the stimulus is called fatigue.
(7) After discharge:
• After reflex contracton, if the stimulation is discontinued, the muscle does not
completely relax at once. It relax gradually. This is due to the fact that the center go
on discharging motor impulses for a brief period, even after the sensory stimuli are
stopped. So, even after cessation of afferent stimulation, these impulses travel for
certain periods.
JCR/Human Physiology Nervous System 93
Properties of reflexes
(8) Rebound phenomenon
• The reflex activities can be inhibited by some methods during certain
period. But, when the inhibition is suddenly removed, the reflex activity
becomes more forceful than the force before inhibition. It is called rebound
phenomenon.
JCR/Human Physiology Nervous System 94
Nerve endings/Receptors
• Receptors are the sensory nerve endings that terminate in the periphery
as bare unmyelinated endings or in the form of specialized capsulated
structures.
• The receptors give response to the stimulus.
• Receptor converts the stimulus in the environment into action potentials
in the nerve fiber.
JCR/Human Physiology Nervous System 95
Classification of receptors
• Generally, the receptors are classified into two types:
• (1) Exteroceptors: which give response to stimuli arising from outside the body
• (a) Cutaneous receptors
• (b) Chemorecepots
• (c) Telereceptors
• (2) Interoceptors: which give response to stimuli arising from within the body
• (a) Visceroceptors
• (b) Proprioceptors
JCR/Human Physiology Nervous System 96
Exteroceptors
1. Cutaneous receptors:
• The receptors situated in the skin are called cutaneous receptors.
• They are also called mechanoceptors because of their response to mechanical
stimuli such as touch, pressure and pain.
2. Chemoreceptors:
• The receptors, which give response to chemical stimuli, are called the
chemoreceptors.
3. Telereceptors:
• Telereceptors give response to stimuli arising away from the body. These receptors
are also called the distance receptos.
JCR/Human Physiology Nervous System 97
Exteroceptors
1. Cutaneous receptors:
• The receptors situated in the skin are
called cutaneous receptors.
• They are also called mechanoceptors
because of their response to
mechanical stimuli.
• Ruffini’s corpuscles: sense heat
• Pacini’s corpuscles: sense pressure
• Merkeis disks: sense touch
• Krause’s bulbs: sense cold
• Free nerve ending/nociceptors: sense
pain
JCR/Human Physiology Nervous System 98
JCR/Human Physiology Nervous System 99
Exteroceptors
2. Chemoreceptors:
• The receptors, which give response to chemical stimuli, are called the
chemoreceptors.
• The sensation of taste and smell is mediated by these receptors
3. Telereceptors:
• Telereceptors give response to stimuli arising away from the body.
• These receptors are also called the distance receptos.
• Vision and Hearing is mediated by these receptors
JCR/Human Physiology Nervous System 100
Interoceptors
1. Visceroceptors:
• The receptors situated in the viscera are called visceroceptors.
• Stretch receptors: in heart
• Baroreceptors: in blood vessels
• Chemoreceptors: in the GI tract
• Osmoreceptors: in the urinary tract
2. Proprioceptors:
• Proprioceptors give response to change in the position of different parts of the
body.
• Receptors are situated in muscle, tendon, ligament, joints, labyrinthine
apparatus
JCR/Human Physiology Nervous System 101
Sensations
• Sensations are FEELINGS aroused by change of environment.
• The different ways by which the body may be aware of its surroundings are called
SENSATIONS.
Sensation mechanism:
For each sensation the following mechanism is involved:
• (a) An appropriate stimulus
• (b) A specific nerve ending-selectively sensitive to that stimulus
• (c) The sensory pathway-carries the impulse to the central nervous system
• (d) The nerve center-the impulse is finally interpreted as a particular sensation
• (e) Psychical center-the ‘meaning’ of the sensation is analyzed and understood.
JCR/Human Physiology Nervous System 102
Properties of sensation
(1) Modality:
-The ability to distinguish the characteristic of a sensation from all other sensations is
known as modality.
(2) Quality:
-Quality means the nature of sensation.
-Sensations of the same modality may vary in quality. For instance, some individuals
cannot distinguish between red and green (color blindness).
(3) Intensity:
-Stronger the stimulus, higher will be frequency and more intense will be the
sensation.
-Two sensation of same quality may differ in intensity. A warm object delivers little
energy and a hot object delivers mush energy to the receptors.
JCR/Human Physiology Nervous System 103
Properties of sensation
(4) Adaptation:
-The structure of muscles and nerve adapt to a constant stimulus.
-The frequency of impulse gradually decreases due to adaptation.
(5) Extent:
-It indicates the area from which the sensation arises.
-Depends upon the number of receptors simultaneously stimulated.
(6) Duration:
-The duration of a sensation may be shorter that that of a stimulation due to
adaptation.
-On the other hand, sensations may outlast the period of stimulation and thereby give
rise to after-sensation.
(7) Localization or projection:
-It is the ability to locate the exact spot from which the sensation arises.
-Sensations are invariably projected either to some part of our own body or to some
part of the environment.
 The nervous system can be divided
into:
• The central nervous system (CNS): Consisting
of brain and spinal cord
• The peripheral nervous system (PNS):
Consisting all the nerves outside brain and
spinal cord
JCR/Human Physiology Nervous System 104
 The Peripheral nervous system(PNS):
• The peripheral nervous system (PNS) consists of
paired cranial and sacral nerves.
• Some of these nerves are sensory (afferent).
 i.e. transmit impulses to the CNS.
• Some are motor nerves (efferent).
 i.e. transmit impulses from the CNS. Some others
are mixed.
JCR/Human Physiology Nervous System 105
 The central nervous system(CNS):
• The central nervous system receives sensory
information through afferent nerves.
• It then processes this information and responds
appropriately by sending impulses through motor
nerves to the effector organs.
• For example, responses to changes in the internal
environment regulate important functions such as
respiration and blood pressure.
JCR/Human Physiology Nervous System 106
 Types of Nerves
• Sensory Nerves – These send messages to the brain
from all the sensory organs.
• Motor Nerves – They carry messages from the brain to
the muscles in the body.
• Mixed Nerves – They carry the sensory and motor
nerves. They help in conducting the incoming sensory
information and also the outgoing information to the
muscle cells.
JCR/Human Physiology Nervous System 107
 Based on which part the nerves connect to the Central Nervous System, they are
classified as:
 Cranial Nerves –
• They start from the brain
and carry messages from
the brain to the rest of
the body.
• Certain nerves are
sensory nerves while
some are mixed nerves.
• The brain communicates
with the body through
the spinal cord and
twelve pairs of cranial
nerves.
JCR/Human Physiology Nervous System 108
Number Name Function
1 olfactory smell
2 optic sight
3 oculomotor Moves eye,pupil
4 trochlear Moves eye
5 trigeminal Face sensation
6 abducens Moves eye
7 facial Moves eye,salivate
8 vestibulocochlear hearing, balance
9 glossopharyngeal taste, swallow
10 vagus heart rate,
digestion
11 accessory moves head
12 hypoglossal moves tongue
 Spinal Nerves
• These nerves originate from the Spinal
Cord.
• They carry messages to and from the
central nervous system.
• They consist of mixed nerves.
Central nervous system
The central nervous system consists of-
• The brain
• The spinal cord.
 Forebrain:
• The cerebrum.
• Hypothalamus.
• Thalamus.
 Midbrain:
• The tectum.
• Tegmentum.
 Hindbrain:
• The cerebellum.
• Medulla.
• Pons.
JCR/Human Physiology Nervous System 109
Temporal lobe
• Understanding language (Wernicke’s area)
• Memory
• Hearing
• Sequencing and organization
Occipital lobe
• Interprets vision (color, light, movement)
• Housing the visual cortex.
Parietal lobe
• Interprets language, words
• Sense of touch, pain, temperature (sensory strip)
• Interprets signals from vision, hearing, motor,
sensory and memory
• Spatial and visual perception
Frontal lobe
• Personality, behavior, emotions
• Judgment, planning, problem solving
• Speech: speaking and writing
• Body movement
• Intelligence, concentration, self awareness
 The brain is roughly split into four lobes:
JCR/Human Physiology Nervous System 110
The cerebellum
The cerebellum is the second largest part of the brain which is
located in the posterior portion of the medulla and pons.
Functions-
 Transfer of information.
 Fine control of the voluntary body movements.
 The cerebellum is responsible for coordinating eye
movements.
 It predicts the future position of the body during a
particular movement.
 The cerebellum is also essential for making fine adjustments
to motor actions.
JCR/Human Physiology Nervous System 111
The Medulla oblongata
The medulla oblongata is a small and the lowest region of the
brain that is enclosed and well protected.
Functions-
• It helps in controlling the involuntary functions of both
respiratory and cardiovascular centers.
• It is involved in regulating life-sustaining functions such as
coughing, sneezing, swallowing, vomiting, salvation,
hiccups, etc.
JCR/Human Physiology Nervous System 112
The Pons
The pons is the major structure of the brain stem present
between the midbrain and medulla oblongata.
Functions-
• It is involved in transferring information between the
cerebellum and motor cortex.
• It controls the magnitude and frequency of the respiration.
• It is also involved in controlling the sleep cycles.
• In addition, the pons is involved in sensations such as the
sense of taste, hearing, and balance.
JCR/Human Physiology Nervous System 113
 Difference between sympathetic and parasympathetic nervous system
JCR/Human Physiology Nervous System 114
Topic Parasympathetic nervous system Sympathetic nervous system
Introduction The parasympathetic nervous system is one of the
two main divisions of the autonomic nervous system
(ANS). Its general function is to control homeostasis
and the body's rest-and-digest response.
The sympathetic nervous system (SNS) is one
of two main divisions of the autonomic
nervous system (ANS). Its general action is to
mobilize the body's fight-or-flight response.
Function Control the body's response while at rest. Control the body's response during perceived
threat.
Activate
response of
Rest and digest. Fight-or-flight.
Heart rate Decreases heart rate. Increases contraction , heart rate.
Salivary gland Saliva production increases. Saliva production decreases.

More Related Content

What's hot

Hypothalamus
HypothalamusHypothalamus
Hypothalamus
WahidahPuteriAbah
 
Pineal gland
Pineal glandPineal gland
Pineal gland
hirparakishan
 
Anatomy and Physiology of Endocrine System
Anatomy and Physiology of Endocrine SystemAnatomy and Physiology of Endocrine System
Anatomy and Physiology of Endocrine System
iffat aisha
 
Pineal gland
Pineal glandPineal gland
Pineal gland
Nisha Mathew
 
Endocrine System
Endocrine SystemEndocrine System
Endocrine System
Mayur Gaikar
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
som allul
 
Endocrine Glands (Structure and Function)
Endocrine Glands (Structure and Function) Endocrine Glands (Structure and Function)
Endocrine Glands (Structure and Function)
Dr. Karri Ramarao
 
Endocrine system
Endocrine system Endocrine system
Endocrine system
Mahesh Thakur
 
1 introduction endocrinology
1 introduction endocrinology1 introduction endocrinology
1 introduction endocrinology
jehadms
 
Physiology of Endocrine System
Physiology of Endocrine System Physiology of Endocrine System
Physiology of Endocrine System
PRANJAL SHARMA
 
Adrenal glands
Adrenal glandsAdrenal glands
Adrenal glands
Lara Patricia Catibog
 
Thyroid gland
Thyroid  glandThyroid  gland
Thyroid gland
academic
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
Adriana Suárez Figueroa
 
Pineal gland
Pineal glandPineal gland
Pineal gland
Lara Patricia Catibog
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
Johny Wilbert
 
Endocrine system & disorders, gland by gland
Endocrine system & disorders, gland by glandEndocrine system & disorders, gland by gland
Endocrine system & disorders, gland by gland
jugafoce
 
19. adrenal glands
19. adrenal glands19. adrenal glands
19. adrenal glands
Nasir Koko
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
Sprint College
 
ENDOCRINE SYSTEM
ENDOCRINE SYSTEMENDOCRINE SYSTEM
ENDOCRINE SYSTEM
arjunsinghkushwaha4
 
Adrenal, pancreas[1]
Adrenal, pancreas[1]Adrenal, pancreas[1]
Adrenal, pancreas[1]
MBBS IMS MSU
 

What's hot (20)

Hypothalamus
HypothalamusHypothalamus
Hypothalamus
 
Pineal gland
Pineal glandPineal gland
Pineal gland
 
Anatomy and Physiology of Endocrine System
Anatomy and Physiology of Endocrine SystemAnatomy and Physiology of Endocrine System
Anatomy and Physiology of Endocrine System
 
Pineal gland
Pineal glandPineal gland
Pineal gland
 
Endocrine System
Endocrine SystemEndocrine System
Endocrine System
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
 
Endocrine Glands (Structure and Function)
Endocrine Glands (Structure and Function) Endocrine Glands (Structure and Function)
Endocrine Glands (Structure and Function)
 
Endocrine system
Endocrine system Endocrine system
Endocrine system
 
1 introduction endocrinology
1 introduction endocrinology1 introduction endocrinology
1 introduction endocrinology
 
Physiology of Endocrine System
Physiology of Endocrine System Physiology of Endocrine System
Physiology of Endocrine System
 
Adrenal glands
Adrenal glandsAdrenal glands
Adrenal glands
 
Thyroid gland
Thyroid  glandThyroid  gland
Thyroid gland
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
 
Pineal gland
Pineal glandPineal gland
Pineal gland
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
 
Endocrine system & disorders, gland by gland
Endocrine system & disorders, gland by glandEndocrine system & disorders, gland by gland
Endocrine system & disorders, gland by gland
 
19. adrenal glands
19. adrenal glands19. adrenal glands
19. adrenal glands
 
Endocrine system
Endocrine systemEndocrine system
Endocrine system
 
ENDOCRINE SYSTEM
ENDOCRINE SYSTEMENDOCRINE SYSTEM
ENDOCRINE SYSTEM
 
Adrenal, pancreas[1]
Adrenal, pancreas[1]Adrenal, pancreas[1]
Adrenal, pancreas[1]
 

Similar to Endocrine System and its glands in brief

Endocrine system
Endocrine systemEndocrine system
Endocrine system
Reach Na
 
Endocrinology
EndocrinologyEndocrinology
Endocrinology
Mujahid Hussain
 
Anatomy of endocrine system
Anatomy of endocrine systemAnatomy of endocrine system
Anatomy of endocrine system
vanajayarrlagadda
 
18. endocrine system
18. endocrine system18. endocrine system
18. endocrine system
Reach Na
 
4 &amp; 5 ther 608 hormones &amp; reproduction
4 &amp; 5 ther 608 hormones &amp; reproduction4 &amp; 5 ther 608 hormones &amp; reproduction
4 &amp; 5 ther 608 hormones &amp; reproduction
farhab dvm
 
Physiology
PhysiologyPhysiology
Physiology
PhysiologyPhysiology
Physiology
PhysiologyPhysiology
A Chapter 7 - Endocronology-1.ppt
A Chapter 7 - Endocronology-1.pptA Chapter 7 - Endocronology-1.ppt
A Chapter 7 - Endocronology-1.ppt
MaruMengeshaWorku18B
 
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.MNEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
velveenamaran
 
Endocrine System~1
Endocrine System~1Endocrine System~1
Endocrine System~1
Alok Kumar
 
endocrine system MSC NURSING PPT PRESENTATION.pptx
endocrine system MSC NURSING PPT PRESENTATION.pptxendocrine system MSC NURSING PPT PRESENTATION.pptx
endocrine system MSC NURSING PPT PRESENTATION.pptx
VISHALDUBEY225290
 
Endocrine system-outline-of-major-players1556
Endocrine system-outline-of-major-players1556Endocrine system-outline-of-major-players1556
Endocrine system-outline-of-major-players1556
Gian Romano
 
12 - Endocrine System.pptx
12 - Endocrine System.pptx12 - Endocrine System.pptx
12 - Endocrine System.pptx
SatyaffPatil
 
Endocrine control system
Endocrine control systemEndocrine control system
Endocrine control system
VadlamudiNamratha
 
Endocrinology pituitary
Endocrinology pituitaryEndocrinology pituitary
Endocrinology pituitary
Liban Qamman
 
Endocrine gland
Endocrine glandEndocrine gland
Endocrine gland
Soneeshah
 
Introduce to endocrine system
Introduce to endocrine systemIntroduce to endocrine system
Introduce to endocrine system
Medical Student
 
Endocrine
EndocrineEndocrine
Endocrine
Jay Patel
 
1. Hypothalamic_Pituitary_Hormones.pptx
1. Hypothalamic_Pituitary_Hormones.pptx1. Hypothalamic_Pituitary_Hormones.pptx
1. Hypothalamic_Pituitary_Hormones.pptx
fatimakhan2112
 

Similar to Endocrine System and its glands in brief (20)

Endocrine system
Endocrine systemEndocrine system
Endocrine system
 
Endocrinology
EndocrinologyEndocrinology
Endocrinology
 
Anatomy of endocrine system
Anatomy of endocrine systemAnatomy of endocrine system
Anatomy of endocrine system
 
18. endocrine system
18. endocrine system18. endocrine system
18. endocrine system
 
4 &amp; 5 ther 608 hormones &amp; reproduction
4 &amp; 5 ther 608 hormones &amp; reproduction4 &amp; 5 ther 608 hormones &amp; reproduction
4 &amp; 5 ther 608 hormones &amp; reproduction
 
Physiology
PhysiologyPhysiology
Physiology
 
Physiology
PhysiologyPhysiology
Physiology
 
Physiology
PhysiologyPhysiology
Physiology
 
A Chapter 7 - Endocronology-1.ppt
A Chapter 7 - Endocronology-1.pptA Chapter 7 - Endocronology-1.ppt
A Chapter 7 - Endocronology-1.ppt
 
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.MNEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
NEURO ENDOCRINOLOGY CONTENT BY VELVEENA.M
 
Endocrine System~1
Endocrine System~1Endocrine System~1
Endocrine System~1
 
endocrine system MSC NURSING PPT PRESENTATION.pptx
endocrine system MSC NURSING PPT PRESENTATION.pptxendocrine system MSC NURSING PPT PRESENTATION.pptx
endocrine system MSC NURSING PPT PRESENTATION.pptx
 
Endocrine system-outline-of-major-players1556
Endocrine system-outline-of-major-players1556Endocrine system-outline-of-major-players1556
Endocrine system-outline-of-major-players1556
 
12 - Endocrine System.pptx
12 - Endocrine System.pptx12 - Endocrine System.pptx
12 - Endocrine System.pptx
 
Endocrine control system
Endocrine control systemEndocrine control system
Endocrine control system
 
Endocrinology pituitary
Endocrinology pituitaryEndocrinology pituitary
Endocrinology pituitary
 
Endocrine gland
Endocrine glandEndocrine gland
Endocrine gland
 
Introduce to endocrine system
Introduce to endocrine systemIntroduce to endocrine system
Introduce to endocrine system
 
Endocrine
EndocrineEndocrine
Endocrine
 
1. Hypothalamic_Pituitary_Hormones.pptx
1. Hypothalamic_Pituitary_Hormones.pptx1. Hypothalamic_Pituitary_Hormones.pptx
1. Hypothalamic_Pituitary_Hormones.pptx
 

More from রেজা তানজিল

Preservatives + types +properties
Preservatives + types +propertiesPreservatives + types +properties
Preservatives + types +properties
রেজা তানজিল
 
Organic chemistry note from bahl
Organic chemistry note from bahlOrganic chemistry note from bahl
Organic chemistry note from bahl
রেজা তানজিল
 
Organic chemistry with its history and effect
Organic chemistry with its history and effectOrganic chemistry with its history and effect
Organic chemistry with its history and effect
রেজা তানজিল
 
Semi solid dosage form
Semi solid dosage formSemi solid dosage form
Semi solid dosage form
রেজা তানজিল
 
Oxidation reduction reactions and reactants
Oxidation reduction reactions and reactantsOxidation reduction reactions and reactants
Oxidation reduction reactions and reactants
রেজা তানজিল
 
Solid and its type with properties
Solid and its type with propertiesSolid and its type with properties
Solid and its type with properties
রেজা তানজিল
 
Aerosol types and properties
Aerosol types and propertiesAerosol types and properties
Aerosol types and properties
রেজা তানজিল
 
Pharmaceutical excipient and its types
Pharmaceutical excipient and its typesPharmaceutical excipient and its types
Pharmaceutical excipient and its types
রেজা তানজিল
 
Amines and types properties
Amines and types properties Amines and types properties
Amines and types properties
রেজা তানজিল
 
Aldehyde ketone and their types and properties
Aldehyde ketone and their types and propertiesAldehyde ketone and their types and properties
Aldehyde ketone and their types and properties
রেজা তানজিল
 
Signaling mechanism with drug actions
Signaling mechanism with drug actionsSignaling mechanism with drug actions
Signaling mechanism with drug actions
রেজা তানজিল
 
Resonance in organic molecules and their types
Resonance in organic molecules and their typesResonance in organic molecules and their types
Resonance in organic molecules and their types
রেজা তানজিল
 
Formulation consideration of drug
Formulation consideration of drugFormulation consideration of drug
Formulation consideration of drug
রেজা তানজিল
 
Significance of tca cycle
Significance of tca cycleSignificance of tca cycle
Significance of tca cycle
রেজা তানজিল
 
Basic concepts of organic chmeistry
Basic concepts of organic chmeistryBasic concepts of organic chmeistry
Basic concepts of organic chmeistry
রেজা তানজিল
 
Enzymes and their types and properties
Enzymes and their types and propertiesEnzymes and their types and properties
Enzymes and their types and properties
রেজা তানজিল
 
Lipid and their types with propertes
Lipid and their types with propertesLipid and their types with propertes
Lipid and their types with propertes
রেজা তানজিল
 
Alcohol phenol ether with types and properties
Alcohol phenol ether with types and propertiesAlcohol phenol ether with types and properties
Alcohol phenol ether with types and properties
রেজা তানজিল
 
Drugs for peptic ulcer
Drugs for peptic ulcerDrugs for peptic ulcer
Drugs for peptic ulcer
রেজা তানজিল
 
Nucleic acid and its types with properties
Nucleic acid and its types with propertiesNucleic acid and its types with properties
Nucleic acid and its types with properties
রেজা তানজিল
 

More from রেজা তানজিল (20)

Preservatives + types +properties
Preservatives + types +propertiesPreservatives + types +properties
Preservatives + types +properties
 
Organic chemistry note from bahl
Organic chemistry note from bahlOrganic chemistry note from bahl
Organic chemistry note from bahl
 
Organic chemistry with its history and effect
Organic chemistry with its history and effectOrganic chemistry with its history and effect
Organic chemistry with its history and effect
 
Semi solid dosage form
Semi solid dosage formSemi solid dosage form
Semi solid dosage form
 
Oxidation reduction reactions and reactants
Oxidation reduction reactions and reactantsOxidation reduction reactions and reactants
Oxidation reduction reactions and reactants
 
Solid and its type with properties
Solid and its type with propertiesSolid and its type with properties
Solid and its type with properties
 
Aerosol types and properties
Aerosol types and propertiesAerosol types and properties
Aerosol types and properties
 
Pharmaceutical excipient and its types
Pharmaceutical excipient and its typesPharmaceutical excipient and its types
Pharmaceutical excipient and its types
 
Amines and types properties
Amines and types properties Amines and types properties
Amines and types properties
 
Aldehyde ketone and their types and properties
Aldehyde ketone and their types and propertiesAldehyde ketone and their types and properties
Aldehyde ketone and their types and properties
 
Signaling mechanism with drug actions
Signaling mechanism with drug actionsSignaling mechanism with drug actions
Signaling mechanism with drug actions
 
Resonance in organic molecules and their types
Resonance in organic molecules and their typesResonance in organic molecules and their types
Resonance in organic molecules and their types
 
Formulation consideration of drug
Formulation consideration of drugFormulation consideration of drug
Formulation consideration of drug
 
Significance of tca cycle
Significance of tca cycleSignificance of tca cycle
Significance of tca cycle
 
Basic concepts of organic chmeistry
Basic concepts of organic chmeistryBasic concepts of organic chmeistry
Basic concepts of organic chmeistry
 
Enzymes and their types and properties
Enzymes and their types and propertiesEnzymes and their types and properties
Enzymes and their types and properties
 
Lipid and their types with propertes
Lipid and their types with propertesLipid and their types with propertes
Lipid and their types with propertes
 
Alcohol phenol ether with types and properties
Alcohol phenol ether with types and propertiesAlcohol phenol ether with types and properties
Alcohol phenol ether with types and properties
 
Drugs for peptic ulcer
Drugs for peptic ulcerDrugs for peptic ulcer
Drugs for peptic ulcer
 
Nucleic acid and its types with properties
Nucleic acid and its types with propertiesNucleic acid and its types with properties
Nucleic acid and its types with properties
 

Recently uploaded

3. Maturity_indices_of_fruits_and_vegetable.pptx
3. Maturity_indices_of_fruits_and_vegetable.pptx3. Maturity_indices_of_fruits_and_vegetable.pptx
3. Maturity_indices_of_fruits_and_vegetable.pptx
UmeshTimilsina1
 
SQL Server Interview Questions PDF By ScholarHat
SQL Server Interview Questions PDF By ScholarHatSQL Server Interview Questions PDF By ScholarHat
SQL Server Interview Questions PDF By ScholarHat
Scholarhat
 
RDBMS Lecture Notes Unit4 chapter12 VIEW
RDBMS Lecture Notes Unit4 chapter12 VIEWRDBMS Lecture Notes Unit4 chapter12 VIEW
RDBMS Lecture Notes Unit4 chapter12 VIEW
Murugan Solaiyappan
 
11. Post harvest quality, Quality criteria and Judgement.pptx
11. Post harvest quality, Quality criteria and Judgement.pptx11. Post harvest quality, Quality criteria and Judgement.pptx
11. Post harvest quality, Quality criteria and Judgement.pptx
UmeshTimilsina1
 
C# Interview Questions PDF By ScholarHat.pdf
C# Interview Questions PDF By ScholarHat.pdfC# Interview Questions PDF By ScholarHat.pdf
C# Interview Questions PDF By ScholarHat.pdf
Scholarhat
 
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
Nguyen Thanh Tu Collection
 
2 Post harvest Physiology of Horticulture produce.pptx
2 Post harvest Physiology of Horticulture  produce.pptx2 Post harvest Physiology of Horticulture  produce.pptx
2 Post harvest Physiology of Horticulture produce.pptx
UmeshTimilsina1
 
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
mansk2
 
Introduction to Google Productivity Tools for Office and Personal Use
Introduction to Google Productivity Tools for Office and Personal UseIntroduction to Google Productivity Tools for Office and Personal Use
Introduction to Google Productivity Tools for Office and Personal Use
Excellence Foundation for South Sudan
 
View Inheritance in Odoo 17 - Odoo 17 Slides
View Inheritance in Odoo 17 - Odoo 17  SlidesView Inheritance in Odoo 17 - Odoo 17  Slides
View Inheritance in Odoo 17 - Odoo 17 Slides
Celine George
 
How To Sell Hamster Kombat Coin In Pre-market
How To Sell Hamster Kombat Coin In Pre-marketHow To Sell Hamster Kombat Coin In Pre-market
How To Sell Hamster Kombat Coin In Pre-market
Sikandar Ali
 
How to Manage Shipping Connectors & Shipping Methods in Odoo 17
How to Manage Shipping Connectors & Shipping Methods in Odoo 17How to Manage Shipping Connectors & Shipping Methods in Odoo 17
How to Manage Shipping Connectors & Shipping Methods in Odoo 17
Celine George
 
Java MCQ Questions and Answers PDF By ScholarHat
Java MCQ Questions and Answers PDF By ScholarHatJava MCQ Questions and Answers PDF By ScholarHat
Java MCQ Questions and Answers PDF By ScholarHat
Scholarhat
 
Parkinson Disease & Anti-Parkinsonian Drugs.pptx
Parkinson Disease & Anti-Parkinsonian Drugs.pptxParkinson Disease & Anti-Parkinsonian Drugs.pptx
Parkinson Disease & Anti-Parkinsonian Drugs.pptx
AnujVishwakarma34
 
Node JS Interview Question PDF By ScholarHat
Node JS Interview Question PDF By ScholarHatNode JS Interview Question PDF By ScholarHat
Node JS Interview Question PDF By ScholarHat
Scholarhat
 
Imagination in Computer Science Research
Imagination in Computer Science ResearchImagination in Computer Science Research
Imagination in Computer Science Research
Abhik Roychoudhury
 
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
ALBERTHISOLER1
 
A beginner’s guide to project reviews - everything you wanted to know but wer...
A beginner’s guide to project reviews - everything you wanted to know but wer...A beginner’s guide to project reviews - everything you wanted to know but wer...
A beginner’s guide to project reviews - everything you wanted to know but wer...
Association for Project Management
 
DepEd School Calendar 2024-2025 DO_s2024_008
DepEd School Calendar 2024-2025 DO_s2024_008DepEd School Calendar 2024-2025 DO_s2024_008
DepEd School Calendar 2024-2025 DO_s2024_008
Glenn Rivera
 
The Cruelty of Animal Testing in the Industry.pdf
The Cruelty of Animal Testing in the Industry.pdfThe Cruelty of Animal Testing in the Industry.pdf
The Cruelty of Animal Testing in the Industry.pdf
luzmilaglez334
 

Recently uploaded (20)

3. Maturity_indices_of_fruits_and_vegetable.pptx
3. Maturity_indices_of_fruits_and_vegetable.pptx3. Maturity_indices_of_fruits_and_vegetable.pptx
3. Maturity_indices_of_fruits_and_vegetable.pptx
 
SQL Server Interview Questions PDF By ScholarHat
SQL Server Interview Questions PDF By ScholarHatSQL Server Interview Questions PDF By ScholarHat
SQL Server Interview Questions PDF By ScholarHat
 
RDBMS Lecture Notes Unit4 chapter12 VIEW
RDBMS Lecture Notes Unit4 chapter12 VIEWRDBMS Lecture Notes Unit4 chapter12 VIEW
RDBMS Lecture Notes Unit4 chapter12 VIEW
 
11. Post harvest quality, Quality criteria and Judgement.pptx
11. Post harvest quality, Quality criteria and Judgement.pptx11. Post harvest quality, Quality criteria and Judgement.pptx
11. Post harvest quality, Quality criteria and Judgement.pptx
 
C# Interview Questions PDF By ScholarHat.pdf
C# Interview Questions PDF By ScholarHat.pdfC# Interview Questions PDF By ScholarHat.pdf
C# Interview Questions PDF By ScholarHat.pdf
 
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
BÀI TẬP BỔ TRỢ 4 KỸ NĂNG TIẾNG ANH LỚP 12 - GLOBAL SUCCESS - FORM MỚI 2025 - ...
 
2 Post harvest Physiology of Horticulture produce.pptx
2 Post harvest Physiology of Horticulture  produce.pptx2 Post harvest Physiology of Horticulture  produce.pptx
2 Post harvest Physiology of Horticulture produce.pptx
 
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
11EHS Term 3 Week 1 Unit 1 Review: Feedback and improvementpptx
 
Introduction to Google Productivity Tools for Office and Personal Use
Introduction to Google Productivity Tools for Office and Personal UseIntroduction to Google Productivity Tools for Office and Personal Use
Introduction to Google Productivity Tools for Office and Personal Use
 
View Inheritance in Odoo 17 - Odoo 17 Slides
View Inheritance in Odoo 17 - Odoo 17  SlidesView Inheritance in Odoo 17 - Odoo 17  Slides
View Inheritance in Odoo 17 - Odoo 17 Slides
 
How To Sell Hamster Kombat Coin In Pre-market
How To Sell Hamster Kombat Coin In Pre-marketHow To Sell Hamster Kombat Coin In Pre-market
How To Sell Hamster Kombat Coin In Pre-market
 
How to Manage Shipping Connectors & Shipping Methods in Odoo 17
How to Manage Shipping Connectors & Shipping Methods in Odoo 17How to Manage Shipping Connectors & Shipping Methods in Odoo 17
How to Manage Shipping Connectors & Shipping Methods in Odoo 17
 
Java MCQ Questions and Answers PDF By ScholarHat
Java MCQ Questions and Answers PDF By ScholarHatJava MCQ Questions and Answers PDF By ScholarHat
Java MCQ Questions and Answers PDF By ScholarHat
 
Parkinson Disease & Anti-Parkinsonian Drugs.pptx
Parkinson Disease & Anti-Parkinsonian Drugs.pptxParkinson Disease & Anti-Parkinsonian Drugs.pptx
Parkinson Disease & Anti-Parkinsonian Drugs.pptx
 
Node JS Interview Question PDF By ScholarHat
Node JS Interview Question PDF By ScholarHatNode JS Interview Question PDF By ScholarHat
Node JS Interview Question PDF By ScholarHat
 
Imagination in Computer Science Research
Imagination in Computer Science ResearchImagination in Computer Science Research
Imagination in Computer Science Research
 
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
Brigada Eskwela 2024 PowerPoint Update for SY 2024-2025
 
A beginner’s guide to project reviews - everything you wanted to know but wer...
A beginner’s guide to project reviews - everything you wanted to know but wer...A beginner’s guide to project reviews - everything you wanted to know but wer...
A beginner’s guide to project reviews - everything you wanted to know but wer...
 
DepEd School Calendar 2024-2025 DO_s2024_008
DepEd School Calendar 2024-2025 DO_s2024_008DepEd School Calendar 2024-2025 DO_s2024_008
DepEd School Calendar 2024-2025 DO_s2024_008
 
The Cruelty of Animal Testing in the Industry.pdf
The Cruelty of Animal Testing in the Industry.pdfThe Cruelty of Animal Testing in the Industry.pdf
The Cruelty of Animal Testing in the Industry.pdf
 

Endocrine System and its glands in brief

  • 1.  Endocrine System • The endocrine system is a chemical messenger system comprising feedback loops of hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. • In humans, the major endocrine glands are the thyroid gland and the adrenal glands. • In vertebrates, the hypothalamus is the neural control centre for all endocrine systems. The study of the endocrine system and its disorders is known as endocrinology. 1JCR - Endocrine System
  • 2. 2 Intercellular Chemical Signals • Hormones: type of intercellular signal. Produced by cells of endocrine glands, enter circulatory system, and affect distant cells; e.g., estrogen • Autocrine: released by cells and have a local effect on same cell type from which chemical signals released; e.g., prostaglandin • Paracrine: released by cells and affect other cell types locally without being transported in blood; e.g., somatostatin • Pheromones: secreted into environment and modify behavior and physiology; e.g., sex pheromones • Neurohormone: produced by neurons and function like hormones; e.g., oxytocin • Neurotransmitter or neuromodulator: produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells; e.g., acetylcholine. JCR - Endocrine System
  • 3.  Functional Classification of Intercellular Chemical Signals JCR - Endocrine System 3
  • 4. 4  Functional Classification of Intercellular Chemical Signals JCR - Endocrine System
  • 5.  Hypothalamic Control of the Endocrine System • Master control center of the endocrine system • Hypothalamus oversees most endocrine activity: – special cells in the hypothalamus secrete hormones that influence the secretory activity of the anterior pituitary gland • called regulatory hormones • releasing hormones (RH) • inhibiting hormones (IH) • Hypothalamus has indirect control over these endocrine organs. JCR - Endocrine System 5
  • 6. JCR - Endocrine System 6
  • 7.  Hypothalamic Control of the Endocrine System • Hypothalamus produces two hormones that are transported to and stored in the posterior pituitary. – oxytocin (paraventicular nucleus) – antidiuretic hormone (ADH) (supraoptic nucleus) • Hypothalamus directly oversees the stimulation and hormone secretion of the adrenal medulla. – An endocrine structure that secretes its hormones in response to stimulation by the sympathetic nervous system. • Some endocrine cells are not under direct control of hypothalamus. JCR - Endocrine System 7
  • 8. JCR - Endocrine System 8
  • 10. Pituitary gland 10JCR - Endocrine System
  • 11. The master gland : • The pituitary gland is called the “master gland” because its hormones regulate other important endocrine glands—including the adrenal, thyroid, and reproductive glands (e.g., ovaries and testes)—and in some cases have direct regulatory effects in major tissues, such as those of the musculoskeletal system. 11JCR - Endocrine System
  • 13.  Anatomy Location • Lies at the base of brain Sella turcica. • Connected with the hypothalamus by the pituitary stalk or hypophyseal stalk. Division • Anterior lobe ( adenohypophysis) • Intermediate lobe ( not present or very small in humans dispersed within anterior lobe) • Posterior lobe ( neurohypophysis) 13JCR - Endocrine System
  • 14.  Lobes of pituitary gland • Anterior pituitary ( adenohypophysis) Consists of three divisions 1. Pars distalis 2. Pars tuberalis 3. Pars intermedia • Posterior pituitary Consist of two parts 1.Infundibular stalks 2.Pars nervosa 14JCR - Endocrine System
  • 17. Pituitary Gland (Hypophysis) • lies inferior to the hypothalamus. • Small, slightly oval gland housed within the hypophyseal fossa of the sphenoid bone. • Connected to the hypothalamus by a thin stalk, the infundibulum. • Partitioned both structurally and functionally into an anterior pituitary and a posterior pituitary. – (called anterior lobes and posterior lobes) JCR - Endocrine System 17
  • 18. The pituitary gland consists of: A) Anterior lobe (adenohypophysis): Consists of: - Pars distalis - Pars tuberalis - Pars intermedia B) Posterior lobe (neurohypophysis): Consists of pars nervosa which is connected by infundibulum (pituitary stalk) to the median eminence (tuber cinereum) of hypothalamus. JCR - Endocrine System 18
  • 19. Pars distalis is formed of: Thick irregular cords of cells + blood sinusoids There are 2 types of cells: a) Chromophobes: About 50% of the cells. They are small, found in groups and have NO GRANULES in their cytoplasm. b) Chromophils: The other 50% of the cells. They have GRANULES in their cytoplasm and are larger than the chromophobes.There are 2 types of chromophil cells: — ACIDOPHILS (10%): have reddish cytoplasm. They secrete growth hormone (GH) & Prolactin (lactogenic) H. — BASOPHILS (40%): have bluish cytoplasm. They secrete TSH, ACTH, FSH & LH. In general basophils are larger in size and stain deeper than the acidophils. JCR - Endocrine System 19
  • 20. Cells and hormones of the anterior pituitary gland & their functions Cell Hormone secreted Function Somatotropes (Acidophilic) Growth H (somatotropin) Stimulates body growth Mammotropes (Acidophilic) Prolactin (PRL) Stimulates milk production & secretion Thyrotropes (Basophilic) Thyroid Stimulating H (TSH) Stimulates production of thyroid H by follicular cells Gonadotropes (Basophilic) -Follicle Stimulating Hormone (FSH) -Luteinizing H (LH) -Stimulates follicular cells in ovary & spermatogenesis in testis. - Stimulates production of estrogen & progesterone from the ovary & testosterone from the testis Corticotropes (Basophilic) Adreno-Cortico Trophic H (ACTH or corticotropin) Stimulates secretion of glucocorticoids & androgens from adrenal cortexJCR - Endocrine System 20
  • 21. Pars nervosa contains: a) Bundles of nerve fibers. b) Cells called pituicytes. c) homogenous intercellular substance: on fixation it precipitates to form Herring’s body. • The bundles of nerve fibers in the pars nervosa arise in the hypothalamus and descend to the posterior lobe forming the hypothalamo- hypophyseal tract (HHT). • The hormones secreted by nerve cells in the hypothalamus travel down along the HHT & accumulate at the end of the tract in pars nervosa as Herring’s bodies. • It secretes Vasopressin or ADH (Anti Diuretic H) & Oxytocin. JCR - Endocrine System 21
  • 22. JCR - Endocrine System 22
  • 23.  Pituitary Gland Blood Supply JCR - Endocrine System 23
  • 24.  Seven Anterior Pituitary Hormones 1. Human growth hormone (hGH) 2. Thyroid-stimulating hormone (TSH) 3. Follicle-stimulating hormone (FSH) 4. Luteinizing hormone (LH) 5. Prolactin (PRL) 6. Adrenocorticotropic hormone (ACTH) 7. Melanocyte-stimulating hormone (MSH) JCR - Endocrine System 24
  • 25. JCR - Endocrine System25
  • 26. Posterior Pituitary JCR - Endocrine System 26
  • 27. Figure : Synthesis, storage, and release of posterior pituitary hormonesJCR - Endocrine System 27
  • 28. Posterior Pituitary – Antidiuretic Hormone (ADH) • Causes kidneys to retain more water • Causes vasoconstriction  increases blood pressure • Dehydration, pain, stress  increase ADH secretion – Oxytocin causes • Smooth muscle contraction of uterus during childbirth • Causes “letdown” of milk from glands to ducts JCR - Endocrine System 28
  • 29.  Posterior Pituitary JCR - Endocrine System 29
  • 30. JCR - Endocrine System 30
  • 31.  Pituitary gland disorders Causes of disorders of pituitary gland • Hyperactivity • Hypoactivity Hyperpituitarism • Hyperfunctioning of anterior pituitary gland - Gigantism and acromegaly • Hyperfunctioning of posterior pituitary gland - Inappropriate release of ADH 31JCR - Endocrine System
  • 32.  Hypopituitarism • Hypo functioning of anterior pituitary Dwarfism. • Hypo functioning of posterior pituitary Diabetes insipidus 32JCR - Endocrine System
  • 33.  Gigantism Characterized signs and symptoms : • Excess Growth of body • Average height is approximately 7-8 feet • Headache due to tumor of pituitary • Hyperglycemia, visual disturbance and pituitary diabetes mellitus. • Cure : Gigantism can be cured by hypopituitarism ( burning cells of anterior pituitary) 33JCR - Endocrine System
  • 35.  Acromegaly Characterized symptom & causes • Enlargement, thickening and broadening of bones. • Particularly extremities of the body. • Hypersecretion of growth hormone, thyroid, parathyroid hormone. • Hypertension, headache and visual disturbance are seen. • Cure : as like as gigantism. 35JCR - Endocrine System
  • 36.  Dwarfism Deficiency of growth hormone in children before growth is completed resulting retarded growth. • Short stature. 36JCR - Endocrine System
  • 37.  Control of Anterior Pituitary Gland Secretions • Anterior pituitary gland is controlled by regulatory hormones secreted by the hypothalamus. • Hormones reach the anterior pituitary via hypothalamo- hypophyseal portal system. – essentially a “shunt” – takes venous blood carrying regulatory hormones from the hypothalamus directly to the anterior pituitary JCR - Endocrine System 37
  • 38. JCR - Endocrine System 38
  • 40. Thyroid gland 40JCR - Endocrine System
  • 41. Thyroid Gland • Located immediately inferior to the thyroid cartilage of the larynx and anterior to the trachea. • Distinctive “butterfly” shape due to its left and right lobes, which are connected at the anterior midline by a narrow isthmus. • Both lobes of the thyroid gland are highly vascularized, giving it an intense reddish coloration. • Regulation of thyroid hormone secretion depends upon a complex thyroid gland–pituitary gland negative feedback process. JCR - Endocrine System 41
  • 42. Thyroid Gland • Follicle cells: – Produce and secrete thyroid hormone – Precursor is stored in colloid • Thyroid hormone – Increases metabolic rate – Important in growth and development. • Parafollicular cells – Produce and secrete calcitonin • Calcitonin – Secreted in response to elevated calcium levels – Reduces blood calcium levels – Acts on osteoblasts. JCR - Endocrine System 42
  • 43. JCR - Endocrine System 43
  • 44. JCR - Endocrine System 44
  • 45. JCR - Endocrine System 45
  • 46. The thyroid gland produces 3 major hormones: • Calcitonin: Reduce the concentration of calcium ions in the blood by aiding the absorption of calcium into the matrix of bones. • Triiodothyronine (T3) • Thyroxine (T4) The hormones T3 and T4 work together to regulate the body’s metabolic rate. Increased levels of T3 and T4 lead to increased cellular activity and energy usage in the body. 46JCR - Endocrine System
  • 48.  Thyroid Hormone Synthesis There are six steps in the synthesis of thyroid hormone- • Active transport of Iodide into the follicular cell via Sodium-Iodide Symporter (NIS). This is actually secondary active transport, and the sodium gradient driving it is maintained by a Sodium-Potassium ATPase. • Thyroglobulin (Tg), a large protein rich in Tyrosine, is formed in follicular ribosomes and placed into secretory vesicles. • Exocytosis of Thyroglobulin into follicle lumen, where it is stored as colloid. Thyroglobulin is the scaffold upon which thyroid hormone is synthesised. 48JCR - Endocrine System
  • 49. • Iodination of the Thyroglobulin. Iodide is made reactive by the enzyme thyroid peroxidase. Iodide binds to the benzene ring on Tyrosine residues of Thyroglobulin. First formed is monoiodotyrosine (MIT) then diiodotyrosine (DIT). • Coupling of MIT and DIT to give Triiodothyronine (T3) hormone and coupling of DIT and DIT to give Tetraiodothyronine (T4) hormone, also known as Thyroxine. • Endocytosis of iodinated thyroglobulin back into the follicular cell. Thyroglobulin undergoes proteolysis in lysosomes to cleave the iodinated tyrosine residues from the larger protein. Free T3 or T4 is then released, and the Thyroglobulin scaffold is recycled. 49JCR - Endocrine System
  • 50.  Secretion of thyroid hormone- • Thyroid hormones are released as part of a hypothalamic- pituitary-thyroid axis. The Hypothalamus detects a low plasma concentration of thyroid hormone and releases Thyrotropin-Releasing Hormone (TRH) into the hypophyseal portal system. • TRH binds to receptors found on thyrotrophic cells of the anterior pituitary gland, causing them to release Thyroid Stimulating Hormone (TSH) into the systemic circulation. TSH binds to TSH receptors on the basolateral membrane of thyroid follicular cells and induces the synthesis and release of thyroid hormone. 50JCR - Endocrine System
  • 51.  Function The thyroid gland is one of the main regulators of metabolism. T3 and T4 typically act via nuclear receptors in target tissues and initiate a variety of metabolic pathways. High levels of them typically cause these processes to occur faster or more frequently. Metabolic processes increased by thyroid hormones include: • Basal Metabolic Rate • Gluconeogenesis • Glycogenolysis • Protein synthesis • Lipogenesis • Thermogenesis 51JCR - Endocrine System
  • 52.  Thyroid Conditions- • Goiter: A general term for thyroid swelling. Goiters can be harmless, or can represent iodine deficiency or a condition associated with thyroid inflammation called Hashimoto’s thyroiditis. • Thyroiditis: Inflammation of the thyroid, usually from a viral infection or autoimmune condition. Thyroiditis can be painful, or have no symptoms at all. • Hyperthyroidism: Excessive thyroid hormone production. Hyperthyroidism is most often caused by Graves disease or an overactive thyroid nodule. • Hypothyroidism: Low production of thyroid hormone. Thyroid damage caused by autoimmune disease is the most common cause of hypothyroidism . 52JCR - Endocrine System
  • 53. • Graves disease: An autoimmune condition in which the thyroid is overstimulated, causing hyperthyroidism. • Thyroid cancer: An uncommon form of cancer, thyroid cancer is usually curable. Surgery, radiation, and hormone treatments may be used to treat thyroid cancer. • Thyroid nodule: A small abnormal mass or lump in the thyroid gland. Thyroid nodules are extremely common. Few are cancerous. They may secrete excess hormones, causing hyperthyroidism, or cause no problems. • Thyroid storm: A rare form of hyperthyroidism in which extremely high thyroid hormone levels cause severe illness 53JCR - Endocrine System
  • 54.  Thyroid function tests- • Thyroid function tests are a series of blood tests used to measure how well your thyroid gland is working. Available tests include the T3, T3RU, T4, and TSH. 54JCR - Endocrine System
  • 55.  T4 & TSH results- • The T4 test and the TSH test are the two most common thyroid function tests. They’re usually ordered together. • The T4 test is known as the thyroxine test. A high level of T4 indicates an overactive thyroid (hyperthyroidism). Symptoms include anxiety, unplanned weight loss, tremors, and diarrhea. Most of the T4 in your body is bound to protein. A small portion of T4 is not and this is called free T4. Free T4 is the form that is readily available for your body to use. Sometimes a free T4 level is also checked along with the T4 test. • The TSH test measures the level of thyroid-stimulating hormone in your blood. The TSH has a normal test range between 0.4 and 4.0 milli-international units of hormone per liter of blood (mIU/L). 55JCR - Endocrine System
  • 56.  T3 result- • The T3 test checks for levels of the hormone triiodothyronine. It’s usually ordered if T4 tests and TSH tests suggest hyperthyroidism. The T3 test may also be ordered if you’re showing signs of an overactive thyroid gland and your T4 and TSH aren’t elevated. • The normal range for the T3 is 100–200 nanograms of hormone per deciliter of blood (ng/dL). Abnormally high levels most commonly indicate a condition called Grave’s disease. This is an autoimmune disorder associated with hyperthyroidism. 56JCR - Endocrine System
  • 57.  Parathyroid Gland 57JCR - Endocrine System
  • 58.  Structure • 4 tiny parathyroid glands, in the neck, on the posterior surface of the thyroid gland. Have 2 superiorly & 2 inferiorly. • Small in size, measuring about 6 mm long, 3 mm wide and 2 mm thick with dark brown color 58JCR - Endocrine System
  • 60.  Histology • Made up of chief cells & oxyphil cells Chief cells • Secrete parathormone Oxyphil cells • Degenerated chief cells and their function is unknown. • May secrete parathormone during physiological condition called parathyroid adenoma. 60JCR - Endocrine System
  • 61.  Parathormone • Secreted by the chief cells of the parathyroid glands. • Essential for the maintenance of blood calcium level within a very narrow critical level. • Maintenance of blood calcium level is necessary because calcium is an inorganic ion for many physiological functions. 61JCR - Endocrine System
  • 62. Chemistry • Parathormone is protein in nature, having 84 amino acids. • It’s Molecular weight in 9,500. Half life & Plasma level • Parathormone has a half-life of 10 minutes. • Normal plasma level of PTH is about 1.5-5.5 mg/dL. 62JCR - Endocrine System
  • 63.  Actions of PTH on Blood Calcium Level • Primary action of the PTH is to maintain the blood calcium level within the critical range of 9-11 mg/dL • PTH control blood calcium level by 1. Reabsorption of Ca from Bones 2. Reabsorption of Ca from renal tubules (Kidney) 3. Absorption of Ca from Gastrointestinal tract 63JCR - Endocrine System
  • 64. On bones • PTH enhances the reabsorption of Ca from the bones by acting on osteoblasts and osteoclasts of the bone. • Increases the number and activity of osteoclasts (bone destroying cells). • Increases collagen synthesis. • Increases alkaline phosphatase activity. • Increases local growth factors: IGF and transforming factors. 64JCR - Endocrine System
  • 65. On Kidney • PTH increases the reabsorption of Ca from the renal tubules along with magnesium ions and hydrogen ions Increases Ca reabsorption mainly from distal convoluted tubule and proximal part of collecting duct. • PTH also increases the formation of 1, 25-di- hydroxycholecalciferol (activated form of vitamin D) from 25-hydroxycholecalciferol in kidneys. • Decreased phosphate, sodium and bicarbonate reabsorption from the proximal tubule. 65JCR - Endocrine System
  • 66. On Gastrointestinal Tract • PTH increases the absorption of Ca ions from the GI tract indirectly. • The activated vitamin D is very essential for the absorption of Ca from the GI tract. • PTH also increase the absorption of PO4 & mg. 66JCR - Endocrine System
  • 67.  Disorders of Parathyroid Gland 67JCR - Endocrine System
  • 68.  Tetany Manifested by neuromuscular excitability due to plasma ionized Ca2+ Causes: a)Hypoparathyroidism b)Alkalemia :Decrease the solubility product of Ca2+& PO4 and leads to reduced ionized Ca2+ & precipitation of CaPO4 c)Decreased Ca2+ absorption from the intestine: 1.Low calcium intake and Excess intake of antacids (peptic ulcer) lead to Ca2+ precipitation and decreased absorption. 68JCR - Endocrine System
  • 69.  Manifestation of Tetany • These depend on the degree of red blood Ca2+ level: 1. Manifest tetany: – Blood Ca2+ level is below 7 mg% (N 9-11 mg%). – Muscular spasms in the hands and feet (Carpo-pedal spasm). 2. Latent tetany: – Blood Ca2+ level is at 7-9 mg%. 69JCR - Endocrine System
  • 70.  Treatment of Tetany 1.IV injection of Ca2+ gluconate during spasm. Stops immediately the tetanic spasms. 2. Calcium level is then maintained by giving vitamin D and administration of oral calcium. 3.Acidifying salts as ammonium chloride help Ca2+ absorption as they increase the ionization of Ca2+. 70JCR - Endocrine System
  • 71.  Islets of Langerhans of Pancreas 71JCR - Endocrine System
  • 72.  Pancreas • A triangular gland, which has both exocrine and endocrine cells, located behind the stomach • Strategic location • Acinar cells produce an enzyme-rich juice used for digestion (exocrine product) • Pancreatic islets (islets of Langerhans) produce hormones involved in regulating fuel storage and use. 72JCR - Endocrine System
  • 74.  Islets of Langerhans • 1 Million islets • 1-2% of the pancreatic mass • Beta (β) cells produce insulin • Alpha (α) cells produce glucagon • Delta (δ) cells produce somatostatin • F cells produce pancreatic polypeptide 74JCR - Endocrine System
  • 76.  Insulin • Hormone of nutrient abundance • A protein hormone consisting of two amino acid chains linked by disulfide bonds • Synthesized as part of proinsulin (86 AA) and then excised by enzymes, releasing functional insulin (51 AA) and C peptide (29 AA). 76JCR - Endocrine System
  • 77.  Insulin Structure 1- Large polypeptide 51 AA (MW 6000) 2- Tow chains linked by disulfide bonds. A chain (21 AA) B chain (30 AA) 3- Disulfide bonds. 77JCR - Endocrine System
  • 79.  Insulin Action on Cells • Insulin is the hormone of abundance. • The major targets for insulin are: – liver – Skeletal muscle – adipose tissue • The net result is fuel storage 79JCR - Endocrine System
  • 80.  Insulin Action on Carbohydrate Metabolism Liver: • Stimulates glucose oxidation • Promotes glucose storage as glycogen • Inhibits glycogenolysis • Inhibits gluconeogenesis Muscle: • Stimulates glucose uptake (GLUT4) • Promotes glucose storage as glycogen 80JCR - Endocrine System
  • 81.  Glucagon • A 29-amino-acid polypeptide hormone that is a potent hyperglycemic agent • Produced by α cells in the pancreas • Its major target is the liver, where it promotes: – Glycogenolysis – the breakdown of glycogen to glucose – Gluconeogenesis – synthesis of glucose from lactic acid and noncarbohydrates – Release of glucose to the blood from liver cells 81JCR - Endocrine System
  • 82.  Physiological Action of Glucagon • Stimulates glycogenolysis, gluconeogenesis & inhabits glycogenesis • Promotes lipolysis & ketogenesis • Increases calorigenesis 82JCR - Endocrine System
  • 83.  Somatostatin • Secreted from D cells of pancreas • Also secreted from hypothalamus & GIT • A peptide hormones with 2 forms, one with 14 AAs & the other with 28 Aas Functions ➤ Inhibits secretion of insulin & glucagon ➤ Inhibits GI motility & GI secretions ➤ Regulates feedback control of gastric emptying 83JCR - Endocrine System
  • 84.  Diabetes Mellitus (DM) • A serious disorder of carbohydrate metabolism • Results from hyposecretion or hypoactivity of insulin • The three cardinal signs of DM are: – Polyuria – huge urine output – Polydipsia – excessive thirst – Polyphagia – excessive hunger and food consumption 84JCR - Endocrine System
  • 85.  Diabetes Mellitus Type l Type 1: beta cells destroyed- no insulin produced chronic fasted state, "melting flesh", ketosis, acidosis, glucosuria, diuresis & coma Diabetes Mellitus Type ll • Over 15 million diabetics in USA- 10% type I, 90% type II • More common is some ethnic groups • Insulin resistance keeps blood glucose too high • Chronic complications: atherosclerosis, renal failure& blindness 85JCR - Endocrine System
  • 87.  Symptoms of Diabetes Mellitus ➤ Hyperglycemia ➤ Polyuria ➤ Polydipsia ➤ Polyphagia ➤ Ketoacidosis ➤ Hyperlipidemia ➤ Muscle wasting ➤ Electrolyte depletion 87JCR - Endocrine System
  • 88.  Diagnosis • Demonstrating persistence hyperglycemia & glycosuria • Glucose Tolerance Test (GTT) – oral is preferred • Estimation of Fasting Blood Glucose (FBG) • FBS more than 126 mg% in more than two occasions confirms DM Treatment • Insulin therapy • Oral hypoglycemic agents • Life style modifications 88JCR - Endocrine System
  • 89. Adrenal Glands 89JCR - Endocrine System
  • 91. Our body has two adrenal (suprarenal) glands, each located on the superior pole of each kidney. Each adrenal gland is Structurally and functionally differentiated into two regions or zones: 1.Adrenal Cortex 2. Adrenal medulla 91JCR - Endocrine System
  • 92.  Adrenal Cortex This is the outer or peripheral zone of the adrenal gland, which makes up the bulk of the gland. The adrenal cortex is divided into three zones. Each zone has a different cellular arrangements and secrets different groups of steroid hormones. 92JCR - Endocrine System
  • 93.  Layers of Adrenal Cortex 1. Zona-glomerulosa 2. Zona-fasciculata 3. Zona-reticulata Zona-glomerulosa: • This is the outermost layer of the adrenal cortex which secrets mineralocorticoid hormones. • Immediately beneath the capsule. • Columnar or pyramidal cells • Arranged in closely packed, rounded, arched cords or small clumps. • Occupy 15% of the adrenal cortex. 93JCR - Endocrine System
  • 94.  Zona-fasciculata : • This is the middle zone of the adrenal cortex which secrets glucocorticoids hormone. • Occupy 65% of the adrenal cortex. • Polyhedral, often binucleated cells with lipid droplets in their cytoplasm. • Cells are also called spongyocytes due to vacuolization. 94JCR - Endocrine System
  • 95.  Zona-reticularis • This is the innermost layer of the adrenal cortex which secrets androgen but in small quantities. • Occupy 7% of the adrenal cortex. • Smaller cells disposed in irregular cords forming anastomosing network. • Presence of lipofuscin pigment granules –large and numerous. 95JCR - Endocrine System
  • 96.  Hormones of the Adrenal cortex The adrenocortical hormones and their functions in the body are classified into three groups: 1. Mineralocorticoids 2. Glucocorticoids 3. Adrenal androgens. Biosynthesis of adrenal hormones: 96JCR - Endocrine System
  • 98.  Mineralocorticoids Mineralocorticoids: – secreted from the adrenal cortex-zona glomerulosa. – Main secreted hormone is aldosterone. – It also secrets deoxy-corticosterone,9-alpha flourocortisol, cortisol, cortisone. Functions: – Maintain balance of electrolytes content of the body fluid. – Increased tubular reabsorption of Na+ ions in the exchange for K+ and H+ ions. 98JCR - Endocrine System
  • 99.  Mineralocorticoids – Act mainly on the distal kidney tubules, salivary glands and sweat glands. – Increase blood volume and cardiac output. – Increase blood pressure. Regulations of aldosterone secretion : – Increased of K+ ions. – Decreased of Na+ ions. – Undefined pituitary factors. – ACTH – Hypotension – Increased renin angiotensin 99JCR - Endocrine System
  • 100.  Glucocorticoids Secreted from adrenal cortex-zona fasciculata. Main secreted hormones are: • Cortisol • Prednisone & methyl prednisone • Corticosterone • Cortisone 100JCR - Endocrine System
  • 101.  Functions Effects in the metabolism of carbohydrates, proteins and lipids. • Stimulation of gluconeogenesis. • Mobilization of amino acids from extra hepatic tissues. • Inhibition of glucose uptake in muscles and adipose tissues. • Stimulation of fat breakdown. . 101JCR - Endocrine System
  • 102.  Functions • Suppress immune response. • Destroying circulating lymphocytes. • Inhibiting mitotic activity. • Controlling secretion of cytokines. – Promotes maturation of lungs and production of surfactants in fetal development 102JCR - Endocrine System
  • 103.  Androgen • Secreted from the adrenal cortex-zona reticularis. • Exhibit actions similar to testosterone. Functions : • Responsible for the development and maintenance of reproductive functions. • Stimulation of secondary sex characteristic. • Stimulates the production of skeletal muscles and bones and RBC. 103JCR - Endocrine System
  • 104. 104 • Regulations of androgen: 1. Controlled by luteinizing hormone (LH) and follicle stimulating hormone(FHS). 2. Prolactin shows an inhibitory effects on androgen secretion. • Adrenal glands disorders : 1. Tumors including pheochromocytomas. Infections 2. Genetic mutations. 3. Cushing's syndrome. 4. Addison’s disease. 5. A problem in another gland, such as pituitary. 6. Hyperaldosteronism. JCR - Endocrine System
  • 105.  Adrenal Medulla • Structure • Biosynthesis of hormones • Functions and regulations • Disorder of adrenal medulla 105JCR - Endocrine System
  • 106. Introduction • The adrenal medulla is part of the adrenal gland it is located at the center of the gland. It is surrounded by adrenal cortex. It is the innermost part of the adrenal gland and it has such type of cells that secrete epinephrine also known as adrenaline and norepinephrine which is known as noradrenaline. It also secretes dopamine at a small amount in response to stimulation by sympathetic preganglionic neurons. • In general adrenal medulla is a less common site of chemically induced degenerative lesions. 106JCR - Endocrine System
  • 107. Structure of adrenal medulla • The adrenal medulla consists of irregularly shaped cells grouped around blood vessels. These cells are intimately connected with the sympathetic division of the autonomic nervous system(ANS). • The cells of the adrenal medulla are derived from the neural crest in contrast to the mesodermal origin of the adrenal cortex. The secretory cells of the adrenal medulla are called chromaffin cells because of the formation of colored polymers of catecholamines after exposure to oxidizing agents such as chromate. • In fact these adrenal medullary cells are modified postganglionic neurons and preganglionic autonomic nerve fibers lead to them directly from the central nervous system.107JCR - Endocrine System
  • 108. Structure of adrenal medulla 108JCR - Endocrine System
  • 109. Functions of adrenal medulla • Biosynthesis of hormones: The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines epinephrine, norepinephrine and dopamine. • Stimulation of the sympathetic nerves to the adrenal medullae causes large quantities of epinephrine and norepinephrine to be released into the circulating blood, and these two hormones in turn are carried in the blood to all tissues of the body. On average, about 80 percent of the secretion is epinephrine and 20 percent is norepinephrine. 109JCR - Endocrine System
  • 110. Functions of adrenal medulla • The circulating epinephrine and norepinephrine have almost the same effects on the different organs as the effects caused by direct sympathetic stimulation, except that the effects last 5 to 10 times as long because both of these hormones are removed from the blood slowly over a period of 2 to 4 minutes. • The circulating norepinephrine causes constriction of most of the blood vessels of the body; it also causes increased activity of the heart, inhibition of the gastrointestinal tract, dilation of the pupils of the eyes, and so forth. 110JCR - Endocrine System
  • 112. Regulatory activity of adrenal medulla • Adrenal medulla is the part of the sympathetic system and is important for the regulation of blood pressure . Catecholamines released from the adrenal medulla also have metabolic effects . The following are the most important effects of catecholamines: • They increase blood pressure , skeletal muscle blood flow, skeletal contractility, heart rate, blood glucose, lipolysis. • They decrease visceral blood flow ,gastrointestinal contractility ,urinary output. 112JCR - Endocrine System
  • 113. Disorder of the adrenal medulla • Pathology within the adrenal medulla and the autonomic nervous system is primarily because of neoplasms. The most common tumour, called pheochromocytoma when located in the adrenal medulla, originates from chromaffin cells and excretes catecholamines. • Those tumours found in extra-adrenal chromaffin cells are sometimes referred to as secreting paragangliomas. Neoplasms may also be of neuronal lineage, such as neuroblastomas and ganglioneuromas. 113JCR - Endocrine System
  • 114. Pheochromocytoma • Pheochromocytoma is a chromaffin cell neoplasm that typically causes symptoms and signs from episodic catecholamine release, including paroxysmal hypertension. • In population-based cancer studies, its frequency is approximately two cases per million of the population. The diagnosis of pheochromocytoma is typically made in the fourth or fifth decade of life without gender differences. 114JCR - Endocrine System
  • 116. Paragangliomas • Extra-adrenal pheochromocytomas can be referred to as paragangliomas. They arise from paraganglionic chromaffin cells in association with sympathetic nerves, and are found in the organ of Zuckerkandl, urinary bladder, chest, neck and at the base of the skull. • They are more common in children than in adults, and are more frequently malignant. As discussed earlier, mutations in the SDH family may predispose to head and neck paragangliomas and pheochromocytoma. 116JCR - Endocrine System
  • 118. Neuroblastomas • Neuroblastomas and ganglioneuromas are tumours of the primitive neuroblast cells from the sympathetic nervous system in ganglia and the adrenal medulla. They may represent a continuum of neuronal maturation and are the most common malignancy found in children, representing 7–10% of all childhood cancers. • Because of their more mature ganglion cells which are histologically benign, ganglioneuromas are often metabolically inactive and asymptomatic. They are found incidentally or with compressive symptoms mostly in the posterior mediastinum or retroperitoneum. 118JCR - Endocrine System
  • 120. Nervous System 1 Nervous System • Nervous system is the most important organization which control and integrates the different body functions and maintains the constancy of internal environment. • A network of billions of nerve cells linked together in a highly organized fashion to form the rapid control center of the body. • Primarily, the nervous system is divided into two parts: (1) Central nervous system (2) Peripheral nervous system JCR/Human Physiology
  • 121. Nervous System 2 Division of nervous system JCR/Human Physiology
  • 122. Nervous System 3 Division of nervous system JCR/Human Physiology
  • 123. Nervous System 4 Neuron • Defined as the structural and functional unit of the nervous system • It is otherwise called nerve cell. • Neuron is different from other cells by two ways: (i) neuron has branches or process called axon and dendrites (ii) neuron does not have centrosome so it cannot undergo division JCR/Human Physiology
  • 124. Nervous System 5 Neuron: structure The neuron is made up of three parts: (1) Nerve cell body or soma (2) Dendrites (3) Axon JCR/Human Physiology
  • 125. JCR/Human Physiology Nervous System 6 Neuron: structure Nerve cell body • The nerve cell body is irregular in shape and is constituted by a mass of cytoplasm called neuroplasm. • The cytoplasm contains a large nucleus, nissl bodies, neurofibrils, mitochondria and golgi apparatus. • The nucleus does not contain centrosome, so they cannot multiply like other cells. • Nissl bodies are present in the soma but not in axon. • Presence of neurofibrils is a characteristic feature of the neurons. Neurofibrils are thread like structures present in the soma.
  • 126. JCR/Human Physiology Nervous System 7 Neuron: structure Dendrites • It is the branched process of the neuron and it is branched repeatedly. • It is conductive in nature. • It transmits impulses towards the nerve cell body. • Usually dendrites are shorter than axon. • Number varies from nil to numerous.
  • 127. JCR/Human Physiology Nervous System 8 Neuron: structure Axon • It is the longer process of the nerve cell. • Arises from axon hillock of the nerve cell body. • Devoid of Nissl granules. • Extends for a long distance away from the nerve cell body. • The length of the longest axon is about one meter.
  • 128. JCR/Human Physiology Nervous System 9 Neuron: Myelin sheath • In a myelinated nerve fiber, the axis cylinder is covered by a thick tubular sheath called myelin sheath. • Does not form a continuous sheath and is absent at regular interval. • The area where the myelin sheath is absent is called node of Ranvier. • Myelin sheath is responsible for the white color of the nerve fibers.
  • 129. JCR/Human Physiology Nervous System 10 Myelin sheath: Functions 1. Myelin sheath is responsible for faster conduction of impulse through the nerve fibers. 2. Myelin sheath has a high insulating capacity. Because of this quality, the myelin sheath restricts the nerve impulse within the single nerve fiber, and prevents the stimulation of neighboring nerve fibers.
  • 130. JCR/Human Physiology Nervous System 11 Myelinogenesis • Myelin sheath is formed from wrapping of Schwann cell around the axis cylinder in many concentric layers. • The process of the formation of myelin sheath is called the myelinogenesis. • In the peripheral nerve, the myelinogenesis starts at 4th month of intrauterine life. It is completed only in the second year after birth. • The axon is first enveloped completely by Schwann cell membrane. • The Schwann cell membrane then gives several turns leaving the axon surrounded by many concentric layers.
  • 131. JCR/Human Physiology Nervous System 12 Myelinogenesis
  • 132. JCR/Human Physiology Nervous System 13 Myelinogenesis • During this repeated wrapping, more and more cytoplasm is pushed to the periphery of the Schwann cell. • When the myelination process is completed, the Schwann cell covers the axon with many layers of plasma membranes. This covering is called a myelin sheath. • The Schwann cell cytoplasm outside the myelin sheath contains the cell nucleus and referred to as the neurolema.
  • 133. JCR/Human Physiology Nervous System 14 Classification of Neurons A. Based on the number of processes that emanate from their cell body, neurons can be classified as: 1. Apolar (have no process) • Apolar neurons are type of neuron which contain only one protoplasmic process extends from cell body. • Such neurons are common in insects. • Apolar neurons are specific to the cerebellum and granule region of the dorsal cochlear nucleus. 2. Unipolar (only axon, i.e., 5th cranial nerve) • A unipolar neurons is a type of neuron in which only one protoplasmic process (neurite) extends from the cell body. • Most neurons are multipolar, generating several dendrites and an axon and there are also many bipolar neurons. • Unipolar neurons that begin as bipolar neurons during development are known as pseudounipolar neurons. • Typically these have special structures for transducing some type of physical stimulus (light, sound, temperature, etc.) into electrical activity, no dendrites, and a single axon that conveys the resulting signals into the spinal cord or brain.
  • 134. 3. Bipolar (both axon and dendrite, i.e., retina) • A bipolar neurone or bipolar cell, is a type of neuron which has two extensions (one axon and one dendrite). • Bipolar cells are specialized sensory neurons for the transmission of special senses. • As such, they are part of the sensory pathways for smell, sight, taste, hearing and vestibular functions. 4. Pseudounipolar • cell body in one side, T-shaped, one branch of T being the dendrite and another branch is axon, found in all spinal ganglia. • A pseudounipolar neuron (pseudo – false, uni – one) is a kind of sensory neuron in the peripheral nervous system. 5. Multipolar • A multipolar neuron is a type of neuron that possesses a single axon and many dendrites, allowing for the integration of a great deal of information from other neurons. • These processes are projections from the nerve cell body. • Multipolar neurons constitute the majority of neurons in the central nervous system. • They include motor neurons and interneurons are most commonly found in the cortex of the brain, the spinal cord, and also in the autonomic ganglia. JCR/Human Physiology Nervous System 15
  • 136. JCR/Human Physiology Nervous System 17 Classification of Neurons B. According to function: 1. Sensory Neuron (Afferent): convey information from tissues and organs into the central nervous system. 2. Motor Neuron (Efferent): transmit signals from the central nervous system to the effector cells/tissue. 3. Interneurons: connect neurons within specific regions of the central nervous system.
  • 137. JCR/Human Physiology Nervous System 18 Nerve fibers • A nerve fiber is a threadlike extension of a nerve cell and consists of an axon (microfilament + microtubule) and myelin sheath (if present) in the nervous system.
  • 138. JCR/Human Physiology Nervous System 19 Classification of nerve fiber Nerve fibers are classified by six methods: (1) Depending upon structure (2) Depending upon distribution (3) Depending upon origin (4) Depending upon function (5) Depending upon the secretion of neurotrnsmittter (6) Depending upon diameter and conduction
  • 139. JCR/Human Physiology Nervous System 20 Classification of nerve fibers (1) Based on the structure, the nerve fibers are classified into two ways: 1. Myelinated nerve fibers: covered by myelin sheath 2. Non-myelinated nerve fibers: do not have myelin sheath.
  • 140. JCR/Human Physiology Nervous System 21 Classification of nerve fibers (2) Based on distribution, the nerve fibers are classified into two ways: 1. Somatic nerve fibers: supply the skeletal muscle of the body. 2. Autonomic or Visceral nerve fibers: supply the various internal organs of the body. (3) Based on origin, the nerve fibers are classified into two ways: 1. Cranial nerve fibers: arising from the brain. 2. Spinal nerve fibers: arising from the spinal cord.
  • 141. JCR/Human Physiology Nervous System 22 Classification of nerve fibers (4) Based on function, the nerve fibers are classified into two ways: 1. Motor or Efferent nerve fibers: carry motor impulses from CNS to PNS. 2. Sensory or Afferent nerve fibers: carry sensory impulses from PNS to CNS. (5) Based on secretion of neurotransmitter, the nerve fibers are classified into two ways: 1. Adrenergic nerve fibers: secrete noradrenaline or norepinephrine. 2. Cholinergic nerve fibers: secrete achetylcholine.
  • 142. JCR/Human Physiology Nervous System 23 Classification of nerve fibers (6) Based on diameter and conduction, the nerve fibers are classified into three major types: 1. Type A nerve fibers: further classified into (i) Type A alpha (ii) Type A beta (iii) Type A gamma and (iv) Type B delta 2. Type B nerve fibers 3. Type C nerve fibers • The diameter (thickness) of the nerve fibers: Type A alpha (12 to 24 μ)> Type A beta> Type A gamma > Type A delta> Type B> Type C (<1.5 μ) • The velocity of conductance of the nerve fibers: Type A alpha (70 to 120 m/s)> Type A beta> Type A gamma > Type A delta> Type B> Type C (0.5 to 2 m/s)
  • 143. JCR/Human Physiology Nervous System 24 Properties of nerve fibers (1) Excitability: The nerve can be stimulated or excited by a suitable stimulus, which may be: -mechanical -thermal -chemical -electrical The stimulus must be adequate to produce the action potential, which is propagated. • Excitability depends upon the following factors: (a) Strength of stimulus (b) Duration of stimulus (c) Frequency of stimulus (d) Injury
  • 144. JCR/Human Physiology Nervous System 25 Properties of nerve fibers (2) Conductivity: Conductivity of nerve fiber shows the following characteristics: (i) Impulse is propagated along a nerve in both directions [but under normal conditions the nerve impulse travels in one direction only-in the motor nerve towards the responding organ; in sensory nerve toward the center] (ii) The nerve impulse is propagated with a definite speed. The conduction velocity depends upon the diameter of the nerve fibers, the thicker fibers showing higher velocity. The velocity also depends on the myelination and on temperature.
  • 145. JCR/Human Physiology Nervous System 26 Properties of nerve fibers 3. All-or-none law: -When a nerve is stimulated by a stimulus with sub-threshold strength, action potential does not develop. If the strength of stimulus is above the sub-threshold level, action potential will develop and response will take place. -If the strength or duration of the stimulus be further increased, no alteration in the response will take place. The action potential remains the same. 4. Refractory period: When the nerve fiber is once excited, it will not respond to a second stimulus for a brief period. This period is called refractory period.
  • 146. JCR/Human Physiology Nervous System 27 Properties of nerve fibers 5. Summation: When one subliminal stimulus is applied, it does not produce any response in the nerve fiber. However, if two or more subliminal stimuli are applied within a short interval, the response is produced. It is because the subliminal stimuli are summed up together. 6. Adaptation: While stimulating a nerve fiber continuously, the excitability of the nerve fiber is maximum in the beginning. Later the response decreases slowly and finally the nerve fiber does not show any response at all. This phenomenon is known as adaptation.
  • 147. JCR/Human Physiology Nervous System 28 Properties of nerve fibers 7. Accommodation: If a stimulus even in stronger strength is applied very slowly to a nerve, then there may have no response only due to lack of attaining the threshold strength. This phenomenon is called accommodation. 8. Indefatigability: A nerve fiber cannot be fatigued, even if it is stimulated continuously for a long time. The reason for this is the nerve fiber can conduct only one action potential at a time. At that time, it is completely refractory and does not conduct another action potential.
  • 148. JCR/Human Physiology Nervous System 29 Neuroglia • Neuroglia or glia is the supporting cell of the nervous system. • They are non excitable and do not transmit nerve impulse. • Compared to the number of neurons, the number of glial cells is 10 to 15 times greater. Classification: (1) Central neuroglial cells (a) Astrocytes (b) Microglia (c) Oligodendrocytes (2) Peripheral neuroglial cells (a) Schwann cell (b) Satellite cell
  • 149. JCR/Human Physiology Nervous System 30 Central neuroglial cells : Astrocytes • Star shaped cells present in all parts of the brain. • Two types: (i) Fibrous astrocytes and (ii) Protoplasmic astrocytes • Fibrous Astrocytes: • Occupy mainly the white matter. • Processes of these cells cover the nerve cells and synapses. • Form the Blood Brain Barrier (BBB) • Protoplasmic Astrocytes: • Present mainly in gray matter.
  • 150. JCR/Human Physiology Nervous System 31 Central neuroglial cells : Astrocytes Functions of Astrocytes: • Form supporting network in brain and spinal cord. • From BBB thereby regulate the entry of substances from blood into brain tissues. • Provide calcium and potassium and regulate neurotransmitter level in synapse. • Regulate recycling of neurotransmitter during synaptic transmission.
  • 151. JCR/Human Physiology Nervous System 32 Central neuroglial cells : Microglia • Derived from monocytes • Enter the tissues of nervous system from blood • Engulf and destroy the microorganisms and cellular debris by phagocytosis
  • 152. JCR/Human Physiology Nervous System 33 Central neuroglial cells : Oligodendrocytes • Cells forming myelin sheath around the nerve fibers in CNS. • Provide support to the CNS by forming a semi-stiff connective tissue between the neurons.
  • 153. JCR/Human Physiology Nervous System 34 Peripheral neuroglial cell: Schwann cell • Major glial cells in PNS. • Provide myelination around the nerve fibers in PNS. • Play important role in nerve regeneration. • Remove cellular debris by their phagocytic activity.
  • 154. JCR/Human Physiology Nervous System 35 Peripheral neuroglial cell : Satellite cells • Present in the exterior surface of PNS neurons. • Provide physical support to the PNS neurons.
  • 155. JCR/Human Physiology Nervous System 36 Action Potential • When two electrodes are connected through a suitable amplifier and placed on the surface of a single axon, no potential difference is observed. • However, if one electrode is inserted into the interior of the cell, a constant potential difference is observed, with the inside negative relative to the outside of the cell at rest. • A membrane potential results from separation of positive and negative charges across the cell membrane. • In resting cell the surface is positively charged and the interior is negatively charged. • In neurons, the resting membrane potential is usually about –70 mV
  • 157. JCR/Human Physiology Nervous System 38 Stages of Action Potential Resting stage: • This is the resting membrane potential before the action potential begins. • The membrane is said to be “polarized” during this stage because of the –70 millivolts negative membrane potential that is present. Depolarization stage: • At this time, the membrane suddenly becomes very permeable to sodium ions, allowing tremendous numbers of positively charged sodium ions to diffuse to the interior of the axon. • The normal polarized stage is immediately neutralized by the inflowing positively charged sodium ions, with the potential rising rapidly in the positive direction. This is called depolarization.
  • 159. JCR/Human Physiology Nervous System 40 Stages of Action Potential Repolarization Stage • After depolarization stage when the sodium channels begin to close and the potassium channels open more than normal. • Then, rapid diffusion of potassium ions to the exterior re-establishes the normal negative resting membrane potential. This is called repolarization of the membrane. • In the last part of repolarisation the rate of fall is being abruptly slowed. This slower fall is known as negative after-potential.
  • 160. JCR/Human Physiology Nervous System 41 Stages of Action Potential Repolarization Stage • After reaching the basal level the wave overshoots slightly but slowly in the hyperpolarisation direction. This is known as positive after potential. • The Absolute Refractory Period: Just after the neuron has generated an action potential, it cannot generate another one. Many sodium channels are inactive and will not open, no matter what voltage is applied to the membrane. Most potassium channels are open. This period is called the absolute refractory period. The neuron cannot generate an action potential because sodium cannot move in through inactive channels and because potassium continues to move out through open voltage-gated channels. A neuron cannot generate an action potential during the absolute refractory period.
  • 161. JCR/Human Physiology Nervous System 42 Stages of Action Potential • The Relative Refractory Period: Immediately after the absolute refractory period, the cell can generate an action potential, but only if it is depolarized to a value more positive than normal threshold. This is true because some sodium channels are still inactive and some potassium channels are still open. This is called the relative refractory period. The cell has to be depolarized to a more positive membrane potential than normal threshold to open enough sodium channels to begin the positive feedback loop. The lengths of the absolute and relative refractory periods are important because they determine how fast neurons can generate action potentials. • Resting state: Resting state is when membrane potential returns to the resting voltage that occurred before the stimulus occurred
  • 162. JCR/Human Physiology Nervous System 43 Propagation of action potential • Conduction of nerve impulse through a myelinated nerve fiber is about 50 times faster than through a nonmyelinated fiber. • This is because the action potential jumps from one node to another node of Ranvier. • This type of jumping of action potential from one node to another is called SALTATORY CONDUCTION.
  • 163. JCR/Human Physiology Nervous System 44 Conduction of nerve impulse
  • 164. JCR/Human Physiology Nervous System 45 Propagation of action potential • The myelin sheath is not permeable to ions. So, the entry of sodium from extracellular fluid into nerve occurs only in the node of Ranvier, where the myelin sheath is absent. • It causes depolarization in the node, and not in the internode. Thus, the depolarization occurs at seccessive nodes. • So, the action potential jumps from one node to another. Hence, it is called SALTATORY CONDUCTION.
  • 165. JCR/Human Physiology Nervous System 46 Synapse • The junction between the two neurons is called synapse. • It is the physiological continuity between two nerve cells.
  • 167. The synapse consists of: a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles, a postsynaptic ending that contains receptor sites for neurotransmitters and, a synaptic cleft or space between the presynaptic and postsynaptic endings. It is about 20nm wide. JCR/Human Physiology Nervous System 48
  • 168. JCR/Human Physiology Nervous System 49 Types of synapse According to the nature of synapse formation: (1) Electrical synapses (2) Chemical synapses According to the nature of connections: (1) Axosomatic (2) Axodendritic (3) Axo-axonic
  • 169. JCR/Human Physiology Nervous System 50 Electrical Synapses • Pre- and postsynaptic neurons joined by gap junctions • Allow local current to flow between adjacent cells. • Rare in CNS or PNS • Found in cardiac muscle and many types of smooth muscle.
  • 170. JCR/Human Physiology Nervous System 51 Chemical synapse • The transfer of information across the synapse are brought about by chemical process. • Neurotransmitter is released from presynaptic neuron which travels the synaptic cleft and bind with the receptors on the postsynaptic neuron which facilitates ion channels opening and produces action potentials.
  • 171. JCR/Human Physiology Nervous System 52 Chemical Synapse
  • 172. JCR/Human Physiology Nervous System 53 Types of synapse • Axosomatic: The presynaptic terminal of the axon ends in the cell body (soma) of the neuron.
  • 173. JCR/Human Physiology Nervous System 54 Types of synapse Axodendritic synapse • The presynaptic fibers of any axon end in the dendrites of the postsynaptic cell. Axo-axonic synapse • The presynaptic axon form synapse with the axon of post synaptic cells. • Rare synapse.
  • 174. JCR/Human Physiology Nervous System 55 Mechanism of synaptic transmission 1. Arrival of action potential on presynaptic neuron opens volage- gated Ca++ channels. 2. Ca2+ influx into presynaptic terminal. 3. Ca2+ acts as intracellular messenger stimulating synaptic vesicles to fuse with membrane and release Neurotransmitter (NT) via exocytosis. 4. NT diffuses across synaptic cleft and binds to receptor on postsynaptic membrane.
  • 175. JCR/Human Physiology Nervous System 56 Mechanism of synaptic transmission
  • 176. JCR/Human Physiology Nervous System 57 Mechanism of synaptic transmission 5. Receptor changes shape of ion channel opening it and changing membrane potential. 6. Opening of all types of ion channels causes a localized depolarization of the membrane and produces an excitatory postsynaptic potential (EPSP). 7. Selective opening of only the smaller ions like K+ and Chloride ions, causing hyperpolarization of the membrane and that constitutes the inhibitory postsynaptic potential (IPSP).
  • 177. JCR/Human Physiology Nervous System 58 Mechanism of synaptic transmission 9. If the EPSP exceeds threshold value, it initiates the propagated action potential in the postsynaptic neuron or muscle action potential (MAP) in most skeletal and cardiac muscle. 10. During the development of the EPSP, simultaneously IPSP may be developed at the same site by incoming action potential from other sources. The propagation of nerve impulse by EPSP is dependent upon the intensity of the postsynaptic potential. 11. NT is quickly destroyed by enzymes or taken back up by astrocytes or presynaptic membrane.
  • 178. JCR/Human Physiology Nervous System 59 Properties of synapse (1) Law of forward conduction/One way conduction: • An impulse is allowed to pass through a synapse in one direction only, i.e., from presynaptic neuron to postsynaptic neuron. (2) Synaptic delay: • During the transmission of impulse via synapse, there is a short delay in transmission. It is called synaptic delay. Synaptic delay in chemical synapse is less than 0.5 millisecond. • The synaptic delay is due to: • Release of neurotransmitter • Movement of neurotransmitter from axon terminal to postsynaptic membrane • Action of neurotransmitter to open the ionic channels in postsynaptic membrane
  • 179. JCR/Human Physiology Nervous System 60 Properties of synapse (3) Fatigue: • The synaptic fatigue is due to exhaustion of transmitter materials from the synaptic vesicles following repeated presynaptic stimulation at faster rate. (4) Summation: • If the stimulus be subminimal, the released neurotransmitter will produce EPSP which will not be sufficient to produce discharge of impulse in the postsynaptic neuron. But if a number of subminimal stimuli be applied, their effects will be summated together and the EPSP will be sufficient to discharge a impulse. • Summation is of two types: • (a) Spatial summation: when many presynaptic terminals are stimulated simultaneously. • (b) Temporal summation: when one presynaptic terminal is stimulated repeatedly.
  • 180. JCR/Human Physiology Nervous System 61 Properties of synapse (5) Inhibition: (A) Postsynaptic inhibition: • The postsynaptic inhibition is due to release of inhibitory NT. • This inhibitory NT change of permeability of the membrane which cause hyperpolarization of the postsynaptic membrane and consequently, the action potential elicited by the excitatory stimulus will fail to occur. (B) Presynaptic inhibition: • Inhibition of a stimulatory neuron before it synapses, by inhibiting Ca2+ entry and blocking downstream processes, preventing neurotransmitter release, and therefore preventing the neuron generating and EPSP post-synaptically.
  • 181. JCR/Human Physiology Nervous System 62 Properties of synapse (6) Synaptic block: • The inhibitory neurotransmitter may be blocked at the synaptic junction producing convulsion. • Strychnine (pesticide) blocks the inhibitory activity and causes reduction or abolition of the IPSP in most of the synaptic junctions. • Tetanus toxin also has got similar effects and produces convulsion by blocking the inhibitory neurotransmitter.
  • 182. JCR/Human Physiology Nervous System 63 Neurotransmitter • Neurotransmitters are endogenous chemicals that act as the mediator for the transmission of nerve impulse from one neuron to another neuron through a synapse. • Neurotransmitters are packaged into synaptic vesicles and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of the synapse. • Release of neurotransmitters usually follows arrival of an action potential at the synapse.
  • 183. JCR/Human Physiology Nervous System 64 Types of neurotransmitter (1) According to the nature (chemistry) of NT (a) Amino acids: • NT of this group are involved fast synaptic transmission and are inhibitory and excitatory in aciton • Examples: • γ-aminobutyric acid (GABA) [inhibitory] • Glutamate (glutamic acid) [excitatory] • Aspartate (aspartic acid) [excitatory] • Glycine [inhibitory] (b) Monoamines: • NT of this group involve in slow synaptic transmission and may be inhibitory and excitatory in action. • Acetylcholine (excitatory and inhibitory) • Serotonin (inhibitory)
  • 184. JCR/Human Physiology Nervous System 65 Types of neurotransmitter (1) According to the nature (chemistry) of NT (c) Catecholamines: • Dopamine (inhibitory) • Epinephrine (Adrenaline) [excitatory & inhibitory] • Norepinephrine (Noradrenaline) [excitatory & inhibitory] (d) Others: • Nitric oxide (excitatory) • Histamine [excitatory]
  • 185. JCR/Human Physiology Nervous System 66 Types of neurotransmitter (2) Based on the activity on postsynaptic neuron (a) Excitatory NT • Responsible for the conduction of impulse from presynaptic neuron to the post synaptic neuron. • Causes depolarization in the postsynaptic neuron. • Causes development of EPSP. • Example: • Acetylcholine • Aspartate • Histamine • Glutamate
  • 186. JCR/Human Physiology Nervous System 67 Types of neurotransmitter (b) Inhibitory NT • Inhibit the conduction of impulse from presynaptic neuron to the post synaptic neuron. • Causes hyperpolarization in the postsynaptic neuron. • Causes development of IPSP • Example: • GABA • Dopamine • Serotonin • Glycine
  • 187. JCR/Human Physiology Nervous System 68 Transport and release of NT • The NT is produced in the cell body of neuron and is transported through the axon. • At the axon terminal, the NT is stored in small packets called vesicles. • Under the influence of a stimulus, these vesicles open and release the NT into the synaptic cleft. • It binds to specific receptors on the surface of the postsynaptic neuron. • The receptors are G proteins, protein kinase or ligand gated receptors.
  • 188. JCR/Human Physiology Nervous System 69 Inactivation of NT • After the execution of the action, neurotransmitter is inactivated by following mechanisms: • (1) It diffuses out of synaptic cleft to the area where it has no action • (2) It is destroyed or disintegrated by specific enzymes • (3) It is engulfed and removed by astrocytes • (4) It is removed by reuptake process, i.e. the neurotransmitter is taken back into the axon terminal from where it was released.
  • 189. Functions of Neurotransmitters 1. Acetylcholine: This neurotransmitter was discovered in the year 1921, by Otto Loewi. It is mainly responsible for stimulating muscles. It activates the motor neurons that control the skeletal muscles. It is also concerned with regulating the activities in certain areas of the brain, which are associated with attention, arousal, learning, and memory. People with Alzheimer's disease are usually found to have a substantially low level of acetylcholine. 2. Dopamine: Dopamine is the neurotransmitter that controls voluntary movements of the body, and is associated with the reward mechanism of the brain. In other words, dopamine regulates the pleasurable emotions. Drugs like cocaine, heroin, nicotine, opium, and even alcohol increase the level of this neurotransmitter. A significantly low level of dopamine is associated with Parkinson's disease, while the patients of schizophrenia are usually found to have excess dopamine in the frontal lobes of their brain. JCR/Human Physiology Nervous System 70
  • 190. 3. Serotonin: Serotonin is an important inhibitory neurotransmitter, which can have a profound effect on emotion, mood, and anxiety. It is involved in regulating sleep, wakefulness, and eating. It plays a role in perception as well. The hallucinogenic drugs like LSD actually bind to the serotonin receptor sites, and thereby block the transmission of nerve impulses, in order to alter sensory experiences. 4. Gamma-aminobutyric Acid (GABA): GABA is an inhibitory neurotransmitter that slows down the activities of the neurons, in order to prevent them from getting over excited. When neurons get over excited, it can lead to anxiety. GABA can thus help prevent anxiety. GABA is a non-essential amino acid, that is produced by the body from glutamate. A low level of GABA can have an association with anxiety disorders. Drugs like Valium work by increasing the level of this neurotransmitter. Alcohol and barbiturates can also influence GABA receptors. JCR/Human Physiology Nervous System 71
  • 191. 5. Glutamate: Glutamate is an excitatory neurotransmitter that was discovered in 1907 by Kikunae Ikeda of Tokay Imperial University. It is the most commonly found neurotransmitter in the central nervous system. Glutamate is mainly associated with functions like learning and memory. An excess of glutamate is however, toxic for the neurons. An excessive production of glutamate may be related to the disease, known as amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease. 6. Epinephrine and Norepinephrine: Epinephrine (also known as adrenaline) is an excitatory neurotransmitter, that controls attention, arousal, cognition, and mental focus. Norepinephrine is also an excitatory neurotransmitter, and it regulates mood and physical and mental arousal. An increased secretion of norepinephrine raises the heart rate and blood pressure. JCR/Human Physiology Nervous System 72
  • 192. 7. Endorphins: Endorphins are the neurotransmitters that resemble opioid compounds, like opium, morphine, and heroin in structure. The effects of endorphins on the body are also quite similar to the effects produced by the opioid compounds. In fact, the name 'endorphin' is actually the short form for 'endogenous morphine'. Like opioids, endorphins can reduce pain, stress, and promote calmness and serenity. The opioid drugs produce similar effects by attaching themselves to the endorphin receptor sites. Endorphins enable some animals to hibernate by slowing down their rate of metabolism, respiration, and heart rate. 8. Melatonin: It is the hormone produced by the pineal gland that also acts as a neurotransmitter. It basically controls the sleep-wake cycle. It is also associated with controlling mood and sexual behavior. The production of melatonin is dependent on light. Light to the retina inhibits the production of melatonin, while darkness has a stimulating effect on its production. JCR/Human Physiology Nervous System 73
  • 193. • 9. Nitric Oxide: It is a gas that acts both as a hormone and neurotransmitter, depending on the specific requirement. It can cause the blood vessels to dilate, besides preventing the formation of clots. This in turn, can promote the circulation of blood. Nitric oxide can increase the level of oxygen in the body, and improve memory, learning, alertness, and concentration. It is also responsible for causing the smooth gastrointestinal muscles to relax. To sum up, neurotransmitters are chemicals that allow the nerves to communicate with each other, and thus, regulate the various functions of the body. A substantially high or low level of these chemicals can alter the functions of the entire nervous system. JCR/Human Physiology Nervous System 74
  • 194.  Reflex- • A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. • When a person accidentally touches a hot object, they automatically jerk their hand away without thinking. • A reflex does not require any thought input. JCR/Human Physiology Nervous System 75
  • 195.  Classification of reflexes- Reflexes Clinical Classification Superficial Deep Visceral Pathological Anatomic Classification Segmental Intersegmental Suprasegmental No . of Synapses Asynaptic Monosynaptic Polysynaptic Bisynaptic Functional Classification Flexor Extensor Righting Postural Withdrawal Conditioned Unconditioned JCR/Human Physiology Nervous System 76
  • 196.  Clinical Classification- • Superficial- stimulating superficial structures. • Deep- stimulating receptors deep in muscle. • Visceral- stimulating receptors in viscera. • Pathological- present only during abnormality. JCR/Human Physiology Nervous System 77
  • 197.  Anatomic Classification- • Segmental- reflex arc pass through one anatomic segment Example- knee jerk • Intersegmental- involve> one segment Example- crossed extensor response • Suprasegmental- involve interaction with suprasegmental components Example- postural reflexes (head-limb) JCR/Human Physiology Nervous System 78
  • 198.  Number of synapses- • Asynaptic- axon reflex • Monosynaptic- stretch reflex • Bisynaptic- reciprocal innervation • Polysynaptic- superficial reflex JCR/Human Physiology Nervous System 79
  • 199.  Functional Classification- • Flexor reflexes • Extensor reflexes • Righting reflexes • Postural reflexes • Withdrawal reflexes JCR/Human Physiology Nervous System 80
  • 200.  Others- • Unconditioned reflexes- inborn or inherent reflexes. • Conditioned reflexes- acquired reflexes. Secretion of saliva when food is kept in mouth is unconditioned reflex. secretion even with thought is conditioned reflex. JCR/Human Physiology Nervous System 81
  • 201.  Reflex arc • The neural pathway that controls the reflexes occurs through the reflex arc. • It acts on an impulse even before it reaches the brain. • There are some stimuli that require an automatic, instantaneous response without the need of conscious thought. The following diagram shows the reflex arc pathway- JCR/Human Physiology Nervous System 82
  • 202. JCR/Human Physiology Nervous System 83 Reflex arc: composition (1) Receptor: It is the end organ, which receives the stimulus. (2) Afferent nerve: Afferent or sensory nerve transmits sensory impulses from the receptor to the center. Composition: A simple reflex arc includes five components: (1) Receptors (2) Afferent/sensory nerve (3) Center (4) Efferent/motor nerve (5) Effector ogran
  • 203. JCR/Human Physiology Nervous System 84 Reflex arc: composition (3) Center: • The center is located in the brain or spinal cord. • The center receives the sensory impulses via afferent nerve fibers and in return, it generates appropriate motor impulses. • Afferent and efferent are connected here by interneurons. (4) Efferent nerve: Efferent or motor nerve transmits motor impulses from the center to the effector organ. (5) Effector organ: The effector organ such as the muscle or gland shows the response to the stimulus.
  • 204. JCR/Human Physiology Nervous System 85 Types of reflex arc (1) Monosynaptic reflex arc: Has only two neurons, i.e, only one synapse.
  • 205. JCR/Human Physiology Nervous System 86 Types of reflex arc (2) Polysynaptic reflex arc: Consists of several neurons and two or more synapses.
  • 206. JCR/Human Physiology Nervous System 87 Types of reflex arc (3) Complex or conditioned reflex arc: • This type of reflex involves the brain. • Salivation on smelling one's favorite food is an example of conditional reflex. The individual recognizes the smell and based on a previous experience, the response (salivation) occurs. • The ringing of the bell is called the conditioned stimulus. The dog had, thus, 'learnt' to associate the sound of the bell to food and this made it salivate at the sound of the bell.
  • 207. JCR/Human Physiology Nervous System 88 Types of reflex arc (4) Asynaptic reflex or Axon reflex arc: • The reflex arc has neither an integration center nor any synapse. • Axon reflexes are important in a lot of physiological and physiopathological processes from regulation of skin blood flow and sweating to inflammation and pain, from itch to asthma bronchiale and allergic rhinitis. • This is not a true reflex arc.
  • 208. JCR/Human Physiology Nervous System 89 Properties of reflexes (1) One way conduction: • During any reflex activity, the impulses are transmitted in only one direction through the reflex arc. • The impulse pass from receptors to the center and then from center to effector organ. (2) Reaction time/ synaptic delay: • There is a short interval between the application of stimulus and the onset of reflex response. • This time is lost in crossing the number of synapses in the central nervous system.
  • 209. JCR/Human Physiology Nervous System 90 Properties of reflexes (3) Summation: Both spatial summation and temporal summation play an important role in the facilitation of response during the reflex activity. (i) Spatial summation: when two afferent nerve fibers supplying a muscle are stimulated separately with subminimal stimulus, there is no response. But, if both the nerve fibers are stimulated together with same strength of stimulus, the muscle contracts. It is called spatial summation. (ii) Temporal summation: When one nerve fiber is stimulated repeatedly with subminimal stimuli, these stimuli are summed up to give response in the muscle. It is called temporal summation.
  • 210. JCR/Human Physiology Nervous System 91 Properties of reflexes (4) Occlusion: • When a reflex contraction is produced by simultaneous stimulation of two afferent nerves, the amount of tension (T) in the muscle is less that the sumtotal of the tensions (t1+t2) setup in the same muscle when the two afferent nerves are separately stimulated (i.e., T<t1+t2). • Occlusion is due to the overlapping of the nerve fibers during the distribution. (5) Facilitation: • The passage of a reflex impulse facilitates the transmission of the next impulse (by reducing synaptic resistance). • Each subsequent stimulus seems to exert a better effect than the previous one and makes the passage of the next impulse easier.
  • 211. JCR/Human Physiology Nervous System 92 Properties of reflexes (6) Fatigue: • When a reflex activity is continuously elicited for a long time, the response is reduced slowly and at one stage, the response does not occur. This type of failure to give response to the stimulus is called fatigue. (7) After discharge: • After reflex contracton, if the stimulation is discontinued, the muscle does not completely relax at once. It relax gradually. This is due to the fact that the center go on discharging motor impulses for a brief period, even after the sensory stimuli are stopped. So, even after cessation of afferent stimulation, these impulses travel for certain periods.
  • 212. JCR/Human Physiology Nervous System 93 Properties of reflexes (8) Rebound phenomenon • The reflex activities can be inhibited by some methods during certain period. But, when the inhibition is suddenly removed, the reflex activity becomes more forceful than the force before inhibition. It is called rebound phenomenon.
  • 213. JCR/Human Physiology Nervous System 94 Nerve endings/Receptors • Receptors are the sensory nerve endings that terminate in the periphery as bare unmyelinated endings or in the form of specialized capsulated structures. • The receptors give response to the stimulus. • Receptor converts the stimulus in the environment into action potentials in the nerve fiber.
  • 214. JCR/Human Physiology Nervous System 95 Classification of receptors • Generally, the receptors are classified into two types: • (1) Exteroceptors: which give response to stimuli arising from outside the body • (a) Cutaneous receptors • (b) Chemorecepots • (c) Telereceptors • (2) Interoceptors: which give response to stimuli arising from within the body • (a) Visceroceptors • (b) Proprioceptors
  • 215. JCR/Human Physiology Nervous System 96 Exteroceptors 1. Cutaneous receptors: • The receptors situated in the skin are called cutaneous receptors. • They are also called mechanoceptors because of their response to mechanical stimuli such as touch, pressure and pain. 2. Chemoreceptors: • The receptors, which give response to chemical stimuli, are called the chemoreceptors. 3. Telereceptors: • Telereceptors give response to stimuli arising away from the body. These receptors are also called the distance receptos.
  • 216. JCR/Human Physiology Nervous System 97 Exteroceptors 1. Cutaneous receptors: • The receptors situated in the skin are called cutaneous receptors. • They are also called mechanoceptors because of their response to mechanical stimuli. • Ruffini’s corpuscles: sense heat • Pacini’s corpuscles: sense pressure • Merkeis disks: sense touch • Krause’s bulbs: sense cold • Free nerve ending/nociceptors: sense pain
  • 218. JCR/Human Physiology Nervous System 99 Exteroceptors 2. Chemoreceptors: • The receptors, which give response to chemical stimuli, are called the chemoreceptors. • The sensation of taste and smell is mediated by these receptors 3. Telereceptors: • Telereceptors give response to stimuli arising away from the body. • These receptors are also called the distance receptos. • Vision and Hearing is mediated by these receptors
  • 219. JCR/Human Physiology Nervous System 100 Interoceptors 1. Visceroceptors: • The receptors situated in the viscera are called visceroceptors. • Stretch receptors: in heart • Baroreceptors: in blood vessels • Chemoreceptors: in the GI tract • Osmoreceptors: in the urinary tract 2. Proprioceptors: • Proprioceptors give response to change in the position of different parts of the body. • Receptors are situated in muscle, tendon, ligament, joints, labyrinthine apparatus
  • 220. JCR/Human Physiology Nervous System 101 Sensations • Sensations are FEELINGS aroused by change of environment. • The different ways by which the body may be aware of its surroundings are called SENSATIONS. Sensation mechanism: For each sensation the following mechanism is involved: • (a) An appropriate stimulus • (b) A specific nerve ending-selectively sensitive to that stimulus • (c) The sensory pathway-carries the impulse to the central nervous system • (d) The nerve center-the impulse is finally interpreted as a particular sensation • (e) Psychical center-the ‘meaning’ of the sensation is analyzed and understood.
  • 221. JCR/Human Physiology Nervous System 102 Properties of sensation (1) Modality: -The ability to distinguish the characteristic of a sensation from all other sensations is known as modality. (2) Quality: -Quality means the nature of sensation. -Sensations of the same modality may vary in quality. For instance, some individuals cannot distinguish between red and green (color blindness). (3) Intensity: -Stronger the stimulus, higher will be frequency and more intense will be the sensation. -Two sensation of same quality may differ in intensity. A warm object delivers little energy and a hot object delivers mush energy to the receptors.
  • 222. JCR/Human Physiology Nervous System 103 Properties of sensation (4) Adaptation: -The structure of muscles and nerve adapt to a constant stimulus. -The frequency of impulse gradually decreases due to adaptation. (5) Extent: -It indicates the area from which the sensation arises. -Depends upon the number of receptors simultaneously stimulated. (6) Duration: -The duration of a sensation may be shorter that that of a stimulation due to adaptation. -On the other hand, sensations may outlast the period of stimulation and thereby give rise to after-sensation. (7) Localization or projection: -It is the ability to locate the exact spot from which the sensation arises. -Sensations are invariably projected either to some part of our own body or to some part of the environment.
  • 223.  The nervous system can be divided into: • The central nervous system (CNS): Consisting of brain and spinal cord • The peripheral nervous system (PNS): Consisting all the nerves outside brain and spinal cord JCR/Human Physiology Nervous System 104
  • 224.  The Peripheral nervous system(PNS): • The peripheral nervous system (PNS) consists of paired cranial and sacral nerves. • Some of these nerves are sensory (afferent).  i.e. transmit impulses to the CNS. • Some are motor nerves (efferent).  i.e. transmit impulses from the CNS. Some others are mixed. JCR/Human Physiology Nervous System 105
  • 225.  The central nervous system(CNS): • The central nervous system receives sensory information through afferent nerves. • It then processes this information and responds appropriately by sending impulses through motor nerves to the effector organs. • For example, responses to changes in the internal environment regulate important functions such as respiration and blood pressure. JCR/Human Physiology Nervous System 106
  • 226.  Types of Nerves • Sensory Nerves – These send messages to the brain from all the sensory organs. • Motor Nerves – They carry messages from the brain to the muscles in the body. • Mixed Nerves – They carry the sensory and motor nerves. They help in conducting the incoming sensory information and also the outgoing information to the muscle cells. JCR/Human Physiology Nervous System 107
  • 227.  Based on which part the nerves connect to the Central Nervous System, they are classified as:  Cranial Nerves – • They start from the brain and carry messages from the brain to the rest of the body. • Certain nerves are sensory nerves while some are mixed nerves. • The brain communicates with the body through the spinal cord and twelve pairs of cranial nerves. JCR/Human Physiology Nervous System 108 Number Name Function 1 olfactory smell 2 optic sight 3 oculomotor Moves eye,pupil 4 trochlear Moves eye 5 trigeminal Face sensation 6 abducens Moves eye 7 facial Moves eye,salivate 8 vestibulocochlear hearing, balance 9 glossopharyngeal taste, swallow 10 vagus heart rate, digestion 11 accessory moves head 12 hypoglossal moves tongue
  • 228.  Spinal Nerves • These nerves originate from the Spinal Cord. • They carry messages to and from the central nervous system. • They consist of mixed nerves. Central nervous system The central nervous system consists of- • The brain • The spinal cord.  Forebrain: • The cerebrum. • Hypothalamus. • Thalamus.  Midbrain: • The tectum. • Tegmentum.  Hindbrain: • The cerebellum. • Medulla. • Pons. JCR/Human Physiology Nervous System 109
  • 229. Temporal lobe • Understanding language (Wernicke’s area) • Memory • Hearing • Sequencing and organization Occipital lobe • Interprets vision (color, light, movement) • Housing the visual cortex. Parietal lobe • Interprets language, words • Sense of touch, pain, temperature (sensory strip) • Interprets signals from vision, hearing, motor, sensory and memory • Spatial and visual perception Frontal lobe • Personality, behavior, emotions • Judgment, planning, problem solving • Speech: speaking and writing • Body movement • Intelligence, concentration, self awareness  The brain is roughly split into four lobes: JCR/Human Physiology Nervous System 110
  • 230. The cerebellum The cerebellum is the second largest part of the brain which is located in the posterior portion of the medulla and pons. Functions-  Transfer of information.  Fine control of the voluntary body movements.  The cerebellum is responsible for coordinating eye movements.  It predicts the future position of the body during a particular movement.  The cerebellum is also essential for making fine adjustments to motor actions. JCR/Human Physiology Nervous System 111
  • 231. The Medulla oblongata The medulla oblongata is a small and the lowest region of the brain that is enclosed and well protected. Functions- • It helps in controlling the involuntary functions of both respiratory and cardiovascular centers. • It is involved in regulating life-sustaining functions such as coughing, sneezing, swallowing, vomiting, salvation, hiccups, etc. JCR/Human Physiology Nervous System 112
  • 232. The Pons The pons is the major structure of the brain stem present between the midbrain and medulla oblongata. Functions- • It is involved in transferring information between the cerebellum and motor cortex. • It controls the magnitude and frequency of the respiration. • It is also involved in controlling the sleep cycles. • In addition, the pons is involved in sensations such as the sense of taste, hearing, and balance. JCR/Human Physiology Nervous System 113
  • 233.  Difference between sympathetic and parasympathetic nervous system JCR/Human Physiology Nervous System 114 Topic Parasympathetic nervous system Sympathetic nervous system Introduction The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system (ANS). Its general function is to control homeostasis and the body's rest-and-digest response. The sympathetic nervous system (SNS) is one of two main divisions of the autonomic nervous system (ANS). Its general action is to mobilize the body's fight-or-flight response. Function Control the body's response while at rest. Control the body's response during perceived threat. Activate response of Rest and digest. Fight-or-flight. Heart rate Decreases heart rate. Increases contraction , heart rate. Salivary gland Saliva production increases. Saliva production decreases.