Cns Anatomy.ppt

Nervous system
1
5/15/2023 By Rebuma S

Introduction
• The nervous system is one of the smallest and the
most complex of the 11 body systems.
• The nervous system is an intricate, highly organized network of
billions of neurons and more neuroglia.
• It accounts 2 kg ,about 3% of total body weight
• The nervous system include the brain, cranial nerves and their
branches, the spinal cord, spinal nerves and their branches, ganglia,
enteric plexuses, and sensory receptors
• The brain - which contains about 100 billion neurons.
• Twelve pairs (right and left) of cranial nerves, numbered I through XII,
emerge from the base of the brain.
• Nervous are bundle of axon , connective tissue and blood vessels
2

Spinal cord contains about 100 million neurons.
Thirty-one (31) pairs
pairs of spinal nerves emerge from the spinal cord, each
serving a specific region on the right or left side of the
body.
Ganglia singular is( ganglion) are small masses of nervous
tissue , that are located outside the brain and spinal cord.
the walls of organs of the gastrointestinal tract, extensive net-
works of neuron, enteric plexus,help regulate the digestive
system.
sensory receptor is neurons (specialized cells) that monitor
changes in the internal or external environment,
such as photoreceptors in the retina of the eye
5/15/2023 By Rebuma S 3

Nervous system
Nervous Tissue
• Consist of 2 types of cells
1. Neurons
• Functional, signal conducting cells
2. Neuroglia
• It doesn’t conduct impulse
• Supporting cells & nutrition
 Neurons = nerve cells , the functional and
structural unit of the nervous system
 Specialized to conduct information from one
part of the body to another
4

Major regions of neurons
Cell body (soma) – contain
nucleus other organells and
metabolic center of the cell
One or more slender processes
– fibers that extend from the cell
body (dendrites and axons)
Dendrites An input region –
receive impulse to wards the cell
body
Axon conducting message ,
away from the cell body
A secretory (output) region
(axon terminal) 5

Neuron Anatomy
Cell body
 Contains nucleus ,large
nucleolus, plus most normal
organelles
 Biosynthetic center of the neuron
 Contains many bundles of
protein filaments (neurofibrils)
which help maintain the shape,
structure, and integrity of the
cell.
6

Nervous system
CNS:
 Gray matter cell bodies and unmylenated fibers
 Nuclei – clusters of cell bodies
 White matter tracts, collections of myelinated fibers
PNS:
 Ganglia – clusters of cell bodies
 Nerves-collections of myelinated fibers
• Dendrites and Axons
Dendrites are thin, branched processes whose main
function is to receive incoming signals
Axons are conduct impulses away from the cell body 7

8
Structural classification of neurons
• Structurally, neurons are classified according to the number
of processes extending from the cell body
 Multipolar- neurons usually have several dendrites and one
axon
• Most neurons in the brain and spinal cord
 Bipolar -neurons have one main dendrite and one axon
• They are found in the retina of the eye, in the inner ear, and
in the olfactory (to smell) area of the brain.
Unipolar- neurons have dendrites and one axon that are
• fused together to form a continuous process that emerges
from the cell body

Axolemma - plasma membrane of
axon.
• Surrounded by a myelin sheath, a
wrapping of lipid
• Protects the axon and
• Increases the rate of Action
potential transmission
 Axons end in axonal terminals
 Axonal terminals contain vesicles with
neurotransmitters
 Axonal terminals are separated from
the next neuron by a gap
 Synaptic cleft gap b/n adjacent
neurons
 Synapse junction between nerves
10

Functional Classification of Neurons
Sensory = afferent neurons
 Carry impulses from the sensory receptors to the CNS
 Cutaneous sense organs
 Proprioceptors – detect stretch or tension
 Most sensory neurons are Unipolar in structure.
Motor = efferent neurons
 Carry impulses from the central nervous system to the
muscles or glands
 Most motor neurons are multi-polar in structure.
11

Interneurons (association neurons)
 Found in neural pathways in the central nervous system
 b/n the connection of sensory and motor neurons
 Most interneurons are multipolar in structure.
12

Neuroglia
• Neuroglia are the supporting cells of the central nervous
system .
• These cells are non -excitable and undergo mitotic division.
• The neuroglial cells are of two types - macroglial and
microglial cells.
• The macroglial cells include Astrocytes ,Oligodendrocytes
and Ependymal cells .
• The macroglial cells are derived from the embryonic
neuroectoderm and the microglial cells are mesodermal in
origin.
13

Are supporting nerve cells
6 types of supporting cells (neuroglia)
• 4 &2are found in the CNS and
PNS
Astrocytes
• Star-shaped, abundant, and
versatile
• Guide the migration of
developing neurons
• Function in nutrient transfer
• Support neurons; protect
neurons from harmful
substances; help maintain
prope chemical environment
for generation of nerve
impulses 14

• Microglia -Protect CNS cells from disease by
engulfing invading microbes; migrate to areas of injured
nerve tissue where they clear away debris of dead cells.
• Specialized immune cells that act as the macrophages of
the CNS
• the main phagocytic cell and antigen-presenting cells in the
CNS.
• Ependymal Cells
Some are ciliated which facilitates the movement of
cerebrospinal fluid and circulation
• Oligodendrocytes
Produce the myelin sheath which provides the electrical
insulation for certain neurons in the CNS 16

Neuroglia in the PNS
1. Satellite cells
• Surround clusters of neuronal cell bodies in the PNS
• Support neurons and regulate exchange of material
b/n neural cell bodies and intertistial fluid
2. Schwann cells
• Form myelin sheaths around the axon of larger
nerve fibers in the PNS.
• Vital to neuronal regeneration
17

Organization of the Nervous System
• is divided into
• the Central Nervous System (CNS)
• the brain
• spinal cord
• the Peripheral Nervous System (PNS)
• Includes all nervous tissue
outside the CNS
• Component of PNS
• the cranial nerves and their
branches
• the spinal nerves and their
branches, ganglia and sensory
receptors
18

What covers and protects the CNS ?
• The entire delicate CNS is protected by:
• a bony -cranial bone & vertebrae
• The menings,
• The cerebrospinal fluid (CSF)
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Meninges
are membranes that cover and protect the brain and
spinal cord
They are three layers from outside to inside respectively
• the dura mater
• the arachnoid mater
• the pia mater.
• The dura mater
• is in contact with bone
• is composed primarily of dense connective tissue.
• The cranial dura mater is a double-layered structure.
• The thicker outer periosteal layer adheres tightly to the
cranium, and meningeal layer .
• It extends to S2(second sacral vertebra)
5/15/2023 By Rebuma S 21

• The spinal dura mater is single layered and is similar to the
menigeal layer of the cranial dura mater.
The arachnoid mater
 is the middle of the three meninges.
 The subarachnoid space is located between the
arachnoid mater and the pia mater.
The subarachnoid space contains the CSF
5/15/2023 By Rebuma S 23

The pia mater
 is the deepest meninges attached to the surfaces of the
CNS
It is composed of modified loose fibrous connective
tissue.
It is highly vascular and the ligamentum denticulatum is
the lateral extensions of the pia mater which attaches the
spinal cord to the dura mater.
 Both the pia mater and the arachnoid mater specialize
over the roofs of the ventricles to form the choroid
plexuses.
24

Cerebrospinal fluid
• CSF is secreted by choroidal epithelial cells (ependymal
cells) of the choroid plexuses in the lateral, 3rd, and 4th
ventricles
• Fills the space between
• the arachnoid and pia mater
• ventricles
• central canal of spinal cord.
• Functions:
• Shock absorption
• Support
• Nourishment
25

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• Based on embryological dev’t the brain subdivided in to
three as:
• the forebrain (cerebrum and diencephalons)
• midbrain
• hindbrain (cerebellum, pons, and medulla).
The Cerebrum
• is the largest portion of the brain.
• located in the region of the telencephalon
• It accounts for about 80%
• is responsible for the higher mental functions including
memory and reason
• consists of
• the right hemispheres & left hemispheres

29
The two hemisphere are connected internally by the
corpus callosum
Each hemisphere contains a central cavity called the
lateral ventricle

• The cerebrum consists of two layers.
• cerebral cortex
• The surface layer
• is composed of gray matter( nerve cell bodies.)
• has numerous folds and grooves called convolutions.
• The elevated folds of the convolutions are the cerebral
gyri (singular, gyrus)
• the grooves are the cerebral sulci (singular, sulcus)
• white matter
• Beneath the cerebral cortex
• constitutes the second layer.
30

Lobes of cerebrum
• Each cerebral hemisphere is subdivided into four lobes by
deep sulci called fissures
• The central sulcus (fissure of Rolando)
• b/n the frontal lobe and the parietal lobe.
• The lateral sulcus (fissure of Sylvius)
• b/n the frontal and temporal lobes
31

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Frontal Lobe:
• forms the anterior portion of each hemisphere.
• extends from the central sulcus to the frontal pole
• lies above the lateral sulcus and anterior to the central
sulcus
• concerned with initiating voluntary motor impulses for
the movement of skeletal muscles and responses related
to memory, emotions, reasoning, judgment, verbal
communications, etc

34
Parietal lobe:
• extends from the central sulcus to the occipital lobe
• lies superior to the temporal lobe,
• posterior to the central sulcus.
function : receives and
• integrates sensory information

Temporal lobe:
• lying below the lateral sulcus.
• located below the parietal lobe and the posterior
portion of the frontal lobe.
• is separated from both by the lateral sulcus.
• extends from the temporal pole to the occipital lobe,
• extends from the lateral sulcus to the collateral sulcus.
• contains auditory centers that receive sensory fibers
from the cochlea of the ear
35

Occipital lobe:
• lies posterior to the parieto-occipital sulcus and the
preoccipital notch.
• forms the posterior portion of the cerebrum.
• lies superior to the cerebellum.
• contains the visual cortex
• The principal function of the occipital lobe is concerned
with vision.
36

Functions of Cerebrum:
• Frontal
• voluntary motor functions
• planning, mood, smell and social judgment
• Parietal
• receives and integrates sensory information
• Occipital
• visual center of brain
• Temporal
• areas for hearing, smell, learning, memory, emotional
behavior
37

Special Senses
• Organs of special senses project to specialized regions of
the brain
• Taste - lower end of parietal lobe
• Smell - medial temporal lobe and inferior frontal lobe
• Vision - occipital lobe
• Hearing - superior temporal lobe
• Equilibrium - cerebellum and lateral and central sulcus
• Language
• Includes reading, writing, speaking and understanding
words.
Wernicke area
• permits recognition of spoken and written language and
creates plan of speech
38

Diencephalon
• is the second subdivision of the forebrain and
• Divide in to:
• thalamus
• hypothalamus
• the epithalamus
• The 3rd ventricle forms a cavity on the median plane within
the diencephalon
39

a. Thalamus:
• a paired, large, avoid mass of gray matter, constituting
nearly 80% of the diencephalon.
• Each portion is located immediately below the
respective lateral ventricle.
• Its principal function is to act as a relay center for all
sensory impulses, except smell(olfactory).
41

b. Hypothalamus:
• a small portion of the diencephalon which forms the
floor and part of the lateral walls of the third ventricle.
• The hypothalamus performs numerous vital functions
• hormone secretion (pituitary)
• autonomic NS control
• thermoregulation (thermostat)
• food & water intake (hunger & satiety)
• sleep & circadian rhythms
• memory (mammillary bodies)
• emotional behavior
• anger, aggression, fear,
• pleasure, sex drive, orgasm 42

c. Epithalamus:
• the dorsal portion of the diencephalon that includes a
thin roof over the third ventricle.
• The pineal gland extends outward from the posterior
end of the epithalamus.
• The inside lining of the roof consists of a vascular
choroids plexus where CSF is produced.
43

Pituitary gland (hypophysis)
• is supported by the sella turcica of the sphenoid bone
• positioned on the inferior aspect of the diencephalon
and is attached to the hypothalamus by a stalk-like
structure called the infundibulum.
• The pituitary gland is divided into
• anterior portion (adenohypophysis )
• posterior portion ( the neurohypophysis)
44

3. The brain stem
• The brain stem contains nuclei for autonomic functions
of the body and their connecting tracts.
• It is the portion of the brain that attaches to the spinal
cord it :
• includes
• the midbrain
• pons
• medulla oblongata
45

b. Pons
• b/n the midbrain and the medulla oblongata .
it has two respiratory centers of the pons are called the
apneustic and the pneumotaxic areas.
Medulla oblongata
• function as autonomic centers for controlling vital visceral
functions include
• Cardiac center- adjusts rate & force of heart beat
• Vasomotor center -adjusts blood vessel diameter
• Respiratory centers- control rate & depth of breathing
• Reflex centers- for coughing, sneezing, gagging, swallowing,
vomiting, salivation, sweating, movements of tongue &
head
47

48
Midbrain (Mesencephalon)
is a short section of the brain stem b/n the diencephalon
and the pons.

Cerebellum
• is the second lager structure in the brain.
• occupies the inferior and posterior aspect of the cranial
cavity.
• attached to the brain stem by three paired bundles of
nerve fibers called cerebellar peduncles
• function
• Balance
• coordinating skeletal muscle contractions by recruiting
precise motor units within muscles.
• Impulses for voluntary muscular movement originate in the
cerebral cortex and are coordinated by the cerebellum
49

con.t…
• The cerebellum can be permanently damaged by trauma
or stroke or temporarily affected by drugs such as
alcohol.
• These alterations can produce ataxia is a disturbance in
balance
50

Spinal cord
• extends through the vertebral canal and surrounded by
three meninges
• provides a means of neural communication to and from the
brain through tracts of white matter.
• These are:
• Ascending tracts
• Descending tracts
• serves as a center for spinal reflexes
51

• Location
• in adults, from the foramen magnum to the lower
border of the first lumbar vertebra or (L2)
• in newborns, it extends to the third lumbar(L3)
vertebra.
• is continuous with the medulla oblongata at the
spinomedullary junction.
52

Internal Morphology
• in transverse sections, the spinal cord consists of
central gray matter and peripheral white matter.
A. Gray matter
• is located centrally within the spinal cord
• unmylinated
• is butterfly- or H- shaped in a configuration that varies
according to spinal cord level.
• contains a central canal.
• is divided into three horns or cell columns on each side
54

1. Dorsal/ posterior horn
• receives and processes sensory input
2. Lateral horn
• receives viscerosensory input.
• is found between the dorsal and ventral horns.
3. Ventral/anterior horn
• contains predominately motor nuclei.
• is found at all levels.
56

B . the white matter
• Tracts of the spinal cord
• are divided into ascending and descending pathways.
• Ascending spinal Tracts
• Represent functional pathways that convey sensory
information from soma or viscera to higher levels of
the neural axis.
• Descending spinal Tracts
• are concerned with somatic and visceral motor
activities.
• It is mylinated ,with myelin sheath
58

PNS -subdivided into
I. Somatic nervous system
Consist of :
Sensory neurons- convey information from somatic
receptors and special senses to CNS
Motor neurons –conduct impulses from CNS to skeletal
muscle only- voluntarly
II. The Autonomic Nervous System (ANS).
Consist of:
Sensory neurons- convey information from autonomic
sensory receptors, located primarily in visceral organs to
CNS
Motor neurons- conduct impulse from CNS to smooth
muscle, cardiac muscle and glands- involuntary 59

The peripheral nervous system.
• is that portion of the nervous system outside the CNS.
• The PNS functions to convey impulses to and from the
brain or spinal cord.
• The nerves of the PNS are classified as
• cranial nerves (I-XII) pairs and
• spinal nerve (31) pairs
60

The motor part of the ANS consists of two branches
• sympathetic division
• parasympathetic division.
With few exceptions, effectors receive nerves from both
divisions, and usually they have opposing actions
61
Sympathetic Nervous System
“Fight or Flight”
Exercise, excitement,
emergency, embarrassment
and,ejaculation
Parasympathetic Nervous System
“Rest and Digest”
Digestion, defecation, and
diuresis and erection of clitoris
and penis

Cranial nerves
• There are 12 pairs of cranial nerves
• The cranial nerves are designated by roman numerals
• Their names indicate the structures innervated or the
principal functions of the nerves
I Olfactory nerve – sensory for smell
II Optic nerve – sensory for vision
III Oculomotor nerve – motor fibers to eye muscles
IV Trochlear – motor fiber to eye muscles
V Trigeminal nerve – sensory for the face; motor fibers to
chewing muscles
62

VI Abducens nerve – motor fibers to eye muscles
VII Facial nerve – sensory for taste; motor fibers to the face
VIII Vestibulocochlear nerve – sensory for balance and
hearing
IX Glossopharyngeal nerve – sensory for taste; motor fibers
to the pharynx
X Vagus nerves – sensory and motor fibers for pharynx,
larynx, and viscera
XI Accessory nerve – motor fibers to neck and upper back
XII Hypoglossal nerve – motor fibers to tongue
63

65
No Nerve Type Function
1 Olfactory Sensory Smell
2 Optic Sensory Vision
3 Oculomotor Motor To all muscles of the eye except two: (superior
oblique and lateral rectus)
4 Trochlear Motor To one eye muscle (superior oblique)
5 Trigeminal
Ophtalmic
Maxillary
Mandibular
Mixed: mainly, sensory; small motor
part
-Sensory to mouth, face and
anterior ½ of scalp
- Motor to muscles of mastication.
6 Abducent Motor To one eye muscle (lateral rectus)
7 Facial Mixed: motor, sensory, and
parasympathetic
-Motor to muscles of the face
-Parasympathetic to certain glands in the bead.
-Sensory: taste to anterior 2/3rd of tongue.
8 Auditory
(stato-acoustic)
Sensory (a)Hearing (cochlear part)
(b)Equilibrium (vestibular part)
9 Glossopharyngeal Mixed: motor, sensory, and
parasympathetic
-Sensory for pharynx and tongue
-Motor to one muscle of pharynx (stylopharyngeus)
-Parasympathetic to the parotid gland.
10 Vagus (including
cranial accessory)
Mixed: motor, sensory and
parasympathetic
-Motor to the muscles of the pharynx (except
stylopharyngeus), larynx and palate
-Parasympathetic and sensory to the structures in
the thorax and abdomen.
11 Spinal Accessory Motor To 2 important muscles of the neck:
sternocleidomastoid and trapezius.
12 Hypoglossal Motor To all muscles of the tongue (except palatoglossus)

66
Spinal nerves
• 31 pairs – contain thousands of nerve fibers
• Connect to the spinal cord
• Named for point of tissue from the spinal cord
• 8 pairs of cervical nerves (C1-C8)
• 12 pairs of thoracic nerves (T1-T12)
• 5 pairs of lumbar nerves (L1-L5)
• 5 pairs of sacral nerves (S1-S5)
• 1 pair of coccygeal nerves (Co1)

Components and branches of SN
• The SN is formed by the union of dorsal and ventral
roots resulting in a mixed nerve.
• Dorsal root
• Cell bodies – located in the dorsal root ganglion
• conveys sensory input from the body
• Ventral root
• convey motor output to visceral and somatic motor
neurons.
• joins the dorsal roots to form the spinal nerve
67

• Nerve plexuses
• Except in the thoracic nerves T2-T12, the anterior rami
of the spinal nerves combine and then split again as
networks of nerves referred to as plexuses.
• There are four plexuses:
• the cervical
• the brachial
• the lumbar
• sacral and
• small coccygeal plexus
68

70
Cervical plexus (8pairs)
formed by the anterior rami of the nerves C1 - C4 and a
portion of C5.
Branches of this innervate the skin and muscles of the
neck, and portions of the head and upper part of the
shoulders.
E.g. Fibers from C3, C4, and C5 unite to form the phrenic
nerve (C3-C5) which innervates the diaphragm thereby
causing it to contract during inspiration

71
Brachial plexus
It’s formed by the anterior rami of the nerves C5 – C8 and
T1
Five major nerves
• the axillary- deltoid , teres minor
• radial- posterior compartment of the arm
• musculocutaneus- anterior compartments of the arm
•ulnar -innervates muscles of anterior medial
compartements of the arm
median nerves- anterior compartments of the arm and
some portion of the hand

72
Lumbar plexus
It’s formed by the anterior rami of spinal nerves (L1 - L4)
Branches from this innervate structures of
• the lower part of abdomen
• anterior and medial potions of the lower limb.
E.g. femoral nerve innervates the anterior muscles of the
thigh
• obturator nerve innervates the medial adductor muscles
of the thigh

73
Pudendal , gluteal, sciatic nerves are forms the sacral plexus
The sciatic nerve
is the largest branch of the sacral plexus and is the largest
nerve in the body.
It’s composed of two nerves-
the tibial
common fibular nerves.
Tibial nerve
 innervates most of the posterior thigh and leg muscles
and many of the plantar muscles.
 Common fibular nerve
innervates the anterior and lateral muscles of the leg
and foot

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