nervous system edited .ppt

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 2kg ,about 3% of total body weight
The structures that make up 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.
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Cont…
 Brain - which contains about 100 billion
neurons.
12 (right and left) of cranial nerves, numbered CNI
up to XII, emerge from the base of the brain.
 Spinal cord contains about 100 million
neurons.
 31 pairs of spinal nerves emerge from the spinal
cord, each serving a specific region on the right or
left side of the body
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Cont…
 Ganglia (ganglion) are masses of cell body of
nerve tissue (outside CNS)
 Enteric plexus, extensive networks of neuron in
the walls of organs of the gastrointestinal tract.
 Sensory receptor is specialized neuron cells
that monitor changes in the internal or external
environment,
such as photoreceptors in the retina of the eye
Nervous system is formed from nerve cells
(neurons) and supporting cells
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Functions of the Nervous System
Sensory input :- gathering information or changes occurring
inside and outside of the body and carry into brain and spinal
cord
 Changes in the body are called stimuli
Integration To process and interpret sensory input and decide
if action is needed
Motor output
A response to integrated stimuli
 Carry information(effect) out side the brain and spinal cord
The effect activates muscles or glands
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Two types of cells in nerve tissue
 Consist of 2 types of cells
1. Neurons (nerve cells)
 Functional, signal conducting cells
 The functional and structural unit of the
nervous system
2. Neuroglia
 It doesn’t conduct impulse
 Supporting cells & provide nutrition to
neurons
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Major regions of neurons
 Cell body (soma) – contain nucleus and other organelles,
metabolic center of the cell
 contain one or more slender processes, fibers that extend from
the cell body (dendrites and axons)
 Dendrites: input fiber(bring impulse to wards the cell
body)
 Axon : out put fiber (carry impulse away from cell body)
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Cont…
Cell body
 Contains nucleus with large
nucleolus and organelles like
ribosome
 Biosynthetic center of the
neuron
 Contains many bundles of
protein filaments
(neurofibrils) which help
maintain the shape, structure,
and integrity of the cell.
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Cont..
Cluster of cell body in different parts of NS
form gray matter (central part in brain and
peripheral part in spinal cord)
 Nuclei – clusters of cell bodies in CNS
 Ganglia – clusters of cell bodies
Cluster of myelinated axon forms nerve
bundle
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Structural classification of neurons
According to the number of processes
extending from the cell body; 3 types
of nerves
Multipolar-
neurons usually have several
dendrites and one axon
Most neurons in the brain and
spinal cord
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Cont…
Bipolar
neurons have one main
dendrite and one axon
found in the retina of the
eye, sensory cells in inner
ear, and olfactory cells of
nose
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Cont…
Pseudounipolar
Neurons have dendrites and
one axon that are fused
together to form a one
continuous process that
emerges from the cell body
found in dorsal root ganglia
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Neuron Anatomy
Axolemma
 axon plasma membrane
 Surrounded by a myelin
sheath, a wrapping of lipid
 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
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Cont..
• Myelin sheath
– Is made by wrappings of plasma
membrane of Schwann cells (in
PNS) or oligodendrocytes (in
CNS).
– In its 80% is phospholipid, while
the remaining percentage is made
mainly by protein as nerokeratin
– Each Schwann cell makes a myelin
sheaths segment of 0.08-0.1
mm long separated by the nodes
of Ranvier.
– Myelin sheath Protects the axon
and electrically insulates it
– Increases the rate of Action
potential transmission

Functional Classification of Neurons
1. Sensory (afferent neurons): carry impulses from the sensory
receptors to the CNS
 Cutaneous sense organs and Proprioceptors ; detect stretch or tension
 Most are unipolar
2. Motor (efferent neurons): carry impulses from the central nervous
system to the muscles or glands
 Most motor neurons are multi-polar in structure
3. Interneurons (association neurons):found in neural
pathways in the central nervous system
Connects sensory and motor neurons
Most interneurons are multipolar in structure.
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Neuroglia CNS
 Supporting cells
 Non –excitable cells and undergo mitotic division
 Constitutes half of the total volume of human brain
 Two types : macroglial and microglial cells.
Macroglial cells:
 derived from the embryonic neuroectoderm
 Are Astrocytes, Oligodendrocytes and Ependymal
cells
Microglial cells: monocyte driven cells and
mesodermal in origin
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 4 types of supporting cells in the
CNS: Astrocytes,
Oligodendrocytes,
Ependymal cells and
microglial cells
1. Astrocytes
 Star-shaped, abundant, and
versatile
 Contain cytoplasmic processes
 End as expanded perivascular
feet processes
 Have glycogen
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Astrocytes… cont
Function
• Function in nutrient transfer,
conduit metabolites
• Support neurons; protect
neurons
• Guide the migration of
developing neurons
• Store glycogen
• Make scar tissue after damage,
as replacement gliosis.
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Microglia
• The smallest neuroglia, hence named as microglia, as opposed
to the remaining glial cells collectively called macroglia.
• Have densely stained nucleus, and delicate & wavy processes
with small spines.
• Belong to the mononucleated phagocytic cells
• Protect CNS cells from disease, act as the macrophages of the
CNS

Cont..
3. Ependymal Cells
 Some are ciliated lining ventricles and canals of CNS
 Involved in the production & circulation of the CSF.
4. Oligodendrocytes
 Produce the myelin sheath which provides
the electrical insulation for certain neurons in
the CNS
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Neuroglia in the PNS
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
Schwann cells
 Form myelin sheaths
around the axon of larger
nerve fibers in the PNS
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CNS (Brain and spinal cord)
Embryologic development of brain and spinal cord
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Based on embryological dev’t the brain subdivided in to
three as:
 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
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The two hemisphere are connected internally by the
corpus callosum
 Each hemisphere contains a central cavity called the
lateral ventricle
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Layers of Cerebrum
 Cerebral cortex/gray mater/
The surface layer
 composed neuron 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)
 Cerebral medulla/White matter/
 Beneath the cerebral cortex
 Constitutes the second layer
 Formed from mainly nerve tracts and fibers
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Lobes of cerebrum
Each cerebral hemisphere is subdivided into
five 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
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Frontal Lobe:
 Forms the anterior portion of each
hemisphere
 Extends from the central sulcus to the
frontal pole, above lateral sulcus
 Concerned with initiating voluntary
motor impulses for the movement of
skeletal muscles
 Excution of sensory responses related to
memory, emotions, reasoning,
judgment, verbal communications, etc
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Parietal lobe:
 Extends from the central sulcus to
the occipital lobe, lies superior to the
temporal lobe,
 functions: receives sensory
information from thalamus and
integrates it
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Temporal lobe:
 lying below the lateral sulcus
 Extends from the temporal pole to the
occipital lobe,
 Contains auditory centers that receive sensory
fibers from the cochlea of the ear
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Occipital lobe:
 lies posterior to the parieto-occipital
sulcus
 forms the posterior portion of the
cerebrum.
lies superior to the cerebellum
 Contains the primary and secondary
visual cortex concerned with vision.
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Sensory cortex
 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
 Wernicke area
 Permits recognition of spoken and written language and creates
plan of speech
 located at superior temporal gyrus near posterior end
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Diencephalon
Second subdivision of the forebrain and divide in
to:
1. Thalamus
2. Hypothalamus
3. Epithalamus
 3rd ventricle is the cavity on the median plane
within the diencephalon
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Diencephalon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 43

Relations
Lateral:
Internal
capsule
Medial:
3rd
ventricle
Dorsal:
Lateral
ventricle
Ventral: Exposed on
the base of the brain
Diencephalon 44

Talamus
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 station
for all sensory impulses, except smell
 hence, gateway to cerebral cortex
 integrate & directs information to appropriate
area
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Hypothalamus
 a small portion of the diencephalon which forms the
floor and part of the lateral walls of the third ventricle
Connects nervous system and endocrine system
 The hypothalamus involve: visceromotor,
viscerosensory & endocrine activities
Autonomic NS control
 thermoregulation (thermostat)
 food & water intake (hunger & satiety)
 sleep & circadian rhythms
 memory (mammillary bodies)
 emotional behavior anger, aggression, fear, pleasure, sex
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Epithalamus
the dorsal portion of the
diencephalon that includes
a thin roof over the third
ventricle.
 include pineal gland
extends outward from the
posterior end
 The inside lining of the
roof consists of a vascular
choroids plexus where CSF is
produced. 48
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Pituitary gland (hypophysis)
 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 (neurohypophysis)
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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
 midbrain
 pons
 medulla oblongata
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What brainstem
structures are visible
here?
52

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1. Midrain (Mesencephalon)
 Short section of the brain stem b/n the diencephalon
and the pons
 Contain ascending and descending tracts
 Serves as visual and audition integration and pass
way.
2. Pons
 b/n the midbrain and the medulla oblongata
 bridge connecting Right & Left cerebellar
hemispheres
 Contain sensory and motor nuclei of cranial nerves
V, VI, VII, VIII
 Ascending, descending, and transverse tracts:
 It has two respiratory centers: apneustic and the
pneumotaxic areas
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3. 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
Contian nuclei associated with sensations of touch,
pressure, vibration, and conscious proprioception
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Cerebellum
 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
 Cross section contain
cerebellar cortex and medulla
 Has two hemisphere
connected by white mater
called Vermis
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 Function
 Maintain balance (vestibulocerebellum)
 Planning and Coordination of voluntary
movement(cerebrocerebellum)
 Play an important role in control of muscle tone and
posture of the body (spinocerebellum)
 The cerebellum can be permanently damaged by trauma
or stroke or temporarily affected by drugs such as
alcohol.
 These alterations can produce ataxia (disturbance in
balance)
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Cover of CNS
 The entire delicate CNS is protected by:
a bony -cranial bone & vertebrae
The meninges,
The cerebrospinal fluid (CSF)
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• are a connective tissue
membranes that cover
and protect the brain
and spinal cord
• Has three membranous
layer:
a) the dura mater,
b) the arachnoid mater,
and
c) the pia mater.
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MENINGES

Cont…
1. The Dura mater
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 inner meningeal
layer .
It extends down spinal cord up to S2(second sacral
vertebra)
NB: The spinal dura mater is single layered and is similar to the menigeal
layer of the cranial dura mater.
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2. The arachnoid mater
Is a delicate, impermeable middle layer
 Lying b/n the pia mater (internally) & the dura
mater( externally)
 The subarachnoid space is located between the
arachnoid mater and the pia mater.
 The subarachnoid space contains the CSF
 In certain areas, arachnoid projects into out ward
to form arachnoid villi.
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3. The pia mater
 Deepest highly vascular layer
 It is composed of modified loose fibrous
connective tissue.
 Extends out over the cranial nerves & fuses
with their epineurium
 It is Ligamentum denticulatum is the lateral
extensions of the pia mater which attaches the
spinal cord to the dura mater
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Cerebrospinal fluid(CSF)
 CSF is secreted by choroidal epithelial cells
(ependymal cells) of the choroid plexuses in the
lateral, 3rd, and 4th ventricles
 Fills the space between
 ventricles
 Central canal Spinal
 flows to subarachnoid space through formaen
magendie and luschika
Functions:
Shock absorption, Support , Nourishment
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1-Telencephalon------ lateral ventricals
Monro Foramen(interventricular F)
2-Diencephalon-------third ventricle
3-Mesencephalon----cerebral aqueduct
4- Rhombencephalon--- forth ventricle
5-Spinal cord----- central canal
6- in the end of spinal cord----- terminal
ventricle
Ventricles of CNS
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Spinal Cord
• Ropelike bundle of
nerve tissue within the
vertebral canal (thick as
a finger)
• 31 pairs of spinal
nerves
• Has Cervical & lumbar
enlargements in cord
70

General Structure of Spinal Cord
Principal Parts
• 45 cm in length; 2.5 cm wide
• cervical enlargement - C4-T1 supply upper limbs
• lumbar enlargement - T9-T12 supply lower limbs
• conus medullaris - is tapered tip of spinal cord to
end at L1-L2
• cauda equina - (like horse tail) is L2 to S5 nerve roots
resemble horse’s tail, hang down in the cauda equina
• filum terminale - pia mater anchors cord to coccyx
71

Cont…
 Extends from foramen
magnum to L2 vertebra in
adults
 In newborns, it extends to the
third lumbar(L3) vertebra
 Consists of:
Cervical region
Thoracic region
Lumbar region
Sacral region
Coccygeal region
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Internal Morphology
in transverse sections, the spinal cord consists of
central gray matter and peripheral white matter.
A. Gray matter
 located centrally within the spinal cord
 unmylinated fibers and cell body cluster
 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
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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.
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B . White matter
Tracts of the spinal cord
 are divided into ascending and
descending pathways.
1. Ascending spinal Tracts
Represent functional pathways that
convey sensory information from soma or
viscera to higher levels of the neural axis.
2. Descending spinal Tracts
are concerned with somatic and visceral
motor activities.
 It is mylinated ,with myelin sheath
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PNS
portion of the nervous system outside
the CNS
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
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Cont..
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
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The motor part of the ANS consists of two branches
sympathetic division
 parasympathetic division.
81
 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
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The nerves of the PNS are classified as
 cranial nerves (I-XII) pairs and
 spinal nerve (31) pairs
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CRANIAL NERVES
83
•12 pairs of cranial
nerves.
•All are distributed
in the head & neck,
except CN-X.
•All nerves except
CN-XI originate
from the brain.

CRANIAL NERVES
 The 12 pairs of cranial nerves can be grouped in several ways:
1. according to their central location:
 Cranial nerves I & II, (olfactory & optic nerves), are connected to
forebrain.
 Nerves III & IV (oculomotor & trochlear nerves), are connected with
the midbrain;
 trigeminal (V), abducens (VI), & facial (VII) nerves are located in the
pons;
 Cranial nerves (VIII, IX, X, XI, & XII) are associated with the medulla
oblongata.
 It is important to know this location plan because if a patient exhibits
signs of a specific cranial nerve injury, then the site of the lesion can
be pinpointed.
85

CRANIAL NERVES
2. Another way to group cranial nerves is according to
their functional neuronal components:
 Some have only sensory neurons:
 CN - I, the olfactory nerve, concerned with smell
 CN - II, the optic nerve, which deals with vision
 CN – VIII, the vestibulo-cochlear nerve, concerned with
hearing and equilibriun.
 Some others are composed only of motor neurons:
 CN – III, CN – IV, CN – VI, CN – XI & CN – XII.
 Others are composed of mixed neurons:
 CN – V, CN – VII, CN – IX & CN – X.
86

Purely Sensory Cranial
Nerves
Olfactory Nerves (CN I):
 Originate from receptor cells in
olfactory mucosa.
Optic Nerve (CN II):
 Originate in ganglion nerve layer
(ganglion cells) of retina
• Vestibulo-cochlear nerve) (CN –
VIII)
concerned with hearing & equilibriun
87

Purely Sensory Cranial Nerves: CN-VIII
88

Purely Motor Cranial Nerves: CN-III
 pass into the orbit
thru superior orbital
fissure.
 supply four eyeball
muscles: superior
rectus, inferior rectus,
medial rectus, &
inferior oblique
muscles.
also innervate levator
palpebrae superioris,
responsible for lifting
upper eyelid.
89

Purely Motor Cranial Nerves: CN - IV
CN IV: Trochlear Nerve
• Emerge from posterior surface of
Midbrain & pass via superior orbital
fissure to the orbit
• Supply superior oblique muscle:
 Move eye downward & laterally
• CN - IV Paralysis :- difficulty in
turning eye downward & laterally
90

Purely Motor Cranial Nerves: CN - VI
Abducens Nerve (CN VI):
 Nerve emerges from lower
border of Pons
 supplies lateral rectus m.
• injury to CN VI, causing paralysis
of lateral rectus muscle.
 person unable to abduct eye .
91

Purely Motor Cranial Nerves: CN - XI
Accessory Nerve
(CN XI):
• Purely Motor
• unique cranial nerve: its
spinal roots arise from
motor neurons in upper
five segments of cervical
spinal cord.
• Has spinal & cranial root
 innervate SCM & Trapezius
mm
92

Purely Motor Cranial Nerves: CN - XII
Hypoglossal Nerve (CN - XII):
 Control movement & shape of
tongue
 CN XII Supplies:
 All intrinsic mm of tongue &
 Styloglossus m
 Hyoglossus m
 Genioglossus m
93

Mixed Cranial Nerves: C.N. V
• THE TRIGEMINAL NERVE (V): mixed & largest nerve
– has general sensory fibers & voluntary motor
neurons.
–  sensory fibers convey general sensations of
pain, temperature, touch, pressure, and
proprioception from the face, cornea, mouth, nose
sinuses, tongue, teeth, meninges, outer surface of
the eardrum, and temporomandibular joint.
– motor component :-supply muscles of
mastication—temporalis, masseter, lateral &
medial pterygoids.
94

Mixed Cranial Nerves: C.N. V
95
CN-V has three
branches:
1. V1 or ophthalmic -
pass via superior
orbital fissure
2. V2 -maxillary –
via foramen
rotundum
3. V3- mandibular-
foramen ovale

Mixed Cranial Nerves: C.N. VII
FACIAL NERVE (VII):
Voluntary motor (general
somatic efferent)
– fibers to muscles of
facial expressoin
General sensory
(general somatic
afferent)
– General sensation
from skin of auricle &
from a small area
behind the ear.
96

Mixed Cranial Nerves : C.N. IX
GLOSSOPHARYNGEAL NERVE (IX):
• General sensory neurons from auditory
tube, back of tongue, inner surface of
tympanic membrane, pharynx & carotid
sinus.
• Voluntary motor neurons to
stylopharyngeus muscle.
97

Mixed Cranial Nerves : C.N. X
VAGUS NERVE (X):
 has three major components:
1. Parasympathetic fibers to all autonomic structures of
thorax & abdomen, up to lt colic flexure (e.g. Heart,
coronary arteries, bronchioles, stomach, small & large
intestine, arterioles, glands, liver, pancreas, spleen, etc.)
2. Voluntary motor fibers to muscles of Larynx & pharynx,
(involved in talking & swallowing); also to mm of soft
palate.
3. General sensory fibers: from all the larynx, lower part of
pharynx, viscera, carotid body (chemoreceptor), dura of
posterior cranial fossa.
98

100
Spinal Nerves
 31 pairs and all are mixed
 formed from dorsal and ventral roots of 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)
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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
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Cervical plexus
 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.
 Fibers from C3, C4, and C5 unite to form the
phrenic nerve (C3-C5)(nerve to diaphragm)
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104
 Brachial plexus
It’s formed by the anterior rami of the nerves
C5 – C8 and T1
 Five major nerves
 axillary- deltoid , teres minor
 radial- posterior compartment of the arm
 musculocutaneous- 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
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105
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
Sacral plexus
 Formed by anterior rami of L4,L5 and S1-3
 Pudendal, gluteal, sciatic nerves
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106
Sciatic nerve
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
10/2/2023

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