NERVOUS SYSTEM
DR :WAHEEB AGGAD
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Nervous system
1-It is a system which monitor the changes in the external
and internal environment and start dealing with them
.2-It is formed of highly specialized nerve cells (neurons)
which can:
receive stimuli (from receptors scattered all over the
body)
and deal with them
and finally send the proper impulses to the effectors
which could be muscles or glands.
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N.B
3)The C.N.S
can't regenerate
if injured.
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4) .The functional unit of the
Nervous System is the neuron.
Neuron is the term given to the nerve cell and all
its processes. It is formed of :
 A) cell body has nucleus
 B) two types of processes,
called an axon and dendrites.
 1) the axon is, single, the longest process of the cell
body ,carries nervous impulses away from the cell body.
out side the CNS, the axons(nerve fibers) runs in
groups forming the different nerves of the body
 2)Dendrites are multiple ,the short processes of the
cell body, which carry impulses to wards the cell body.
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Divisions of the Nervous System
The nervous system is divided into
two main parts:
 1) The central nervous system
 2) The peripheral nervous system
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1-The central nervous system,
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1-The central nervous system
is the part of N.S which is
protected by bones ,it is consists
of:
a) The brain
b) spinal cord
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A) The brain
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It is formed of :
a) cerebrum ( the 2 cerebral hemispheres+
the interbrain).
b) Brain stem: which includes:
 Midbrain ( upper part)
 Pons (middle part)
 medulla oblongata (lower part)
c)cerebellum
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A) The brain
is covered by 3 meninges :
1-Dura (the outer layer )
2-arachnoid (the middle)
3-the pia (the inner) matters.
It contains cavities
(Ventricles).
it
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A) The brain

In cross sections, it shows:

a)Grey matter :dark areas which contains the cell
bodies .
 The
grey matter on the surface of the
cerebrum is called the cerebral cortex .
term nucleus is used to describe
any collection of cell bodies which
perform the same function.
 The
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b) White matter :light areas which contain nerve fibers
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(axons) .
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B) The spinal cord
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The spinal cord
Covered by3 meninges like the brain.
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Contains cavity called the central
canal .
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B) The spinal cord
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In cross section ,it shows:
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a) Grey matter: it is arranged in the shape of butter fly
or like letter H.
It projects as 2 dorsal horns (contain sensory neurons )
&2 ventral horns (contain motor neurons) .
A third lateral horn is found only in the segments
which give autonomic outflow.
B) White matter : surrounds the grey matter and
contains nerve fibers which run as tracts.
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B) The spinal cord
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The cord is divided into segments (31):
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a-cervical segments:8.
b-Thoracic segments :12.
c-Lumber segments :5.
d- Sacral segments :5.
e- Single Coccygeal .
N:B.: The right and left parts of the C.N.S. are
connected together by nerve fibers called
commissures.
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2-The peripheral nervous system
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The peripheral nervous system, It is not
protected by bones ,
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It is divided functionally into :
 a-Somatic
nervous system :carries
sensations and controls skeletal muscles .
 b-Autonomic nervous system
:Controls smooth muscle ,heart &glands .
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A-The Somatic nervous System
 The
Somatic nervous System :
which formed of :
 a) cranial nerves :12 pairs of nerves
which arise from the brain.
 b) spinal nerves: 31 pairs of nerves
and their associated ganglia which arise
from the spinal cord ,a pair arises from
each segment.
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A-The Somatic nervous System
a)Cranial Nerves
 There are 12 pairs of cranial nerves that
leave the brain and pass through foramina
in the skull.
 All the nerves are distributed in the head
and neck except the Xth (vagus), which
also supplies structures in the thorax and
abdomen. ) .
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A-The Somatic nervous System
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B) Spinal Nerves
A total of 31 pairs of spinal nerves leave the spinal
cord and pass through intervertebral foramina in the
vertebral column .
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The spinal nerves are named according to the region of the
vertebral column with which they are associated:
8 cervical,
12 thoracic,
5 lumbar,
5 sacral, and
1 coccygeal.
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A-The Somatic nervous System
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N:B
Q )There are eight cervical nerves and only seven
cervical vertebrae and that there is one coccygeal nerve
and four coccygeal vertebrae. WHY?
A) During development, the spinal cord grows slowly
than the vertebral column. In the adult, when growth
STOPED, the lower end of the spinal cord reaches
inferiorly only as far as the lower border of the first
lumbar vertebra( L1
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B) Spinal Nerves
 Each
spinal nerve is connected
to the spinal cord by two roots:
 A) the anterior root and
 B) the posterior root.
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B) Spinal Nerves
 1)The
anterior root (Efferent
fibers )
consists of: Motor fibers, arises from the
anterior horn of gray matter of the
spinal cord.
 carrying motor impulses from the central
nervous system to skeletal muscle and
cause them to contract
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B) Spinal Nerves
 2)
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The posterior root (Afferent fibers)
consists of sensory fibers that are concerned
with conveying information about sensations
of( touch, pain, temperature, and vibrations ) to
the central nervous system, so they are called
sensory fibers ,and ends in the dorsal horn of
the gray matter of the spinal cord .
The cell bodies of these nerve fibers are
situated in a swelling on the posterior root
called the posterior root ganglion
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B) Spinal Nerves
 3)posterior
root ganglion :each
posterior root carries posterior root
ganglion which contains an
aggregation of cell bodies situated in a
swelling.
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B) Spinal Nerves
 At
each intervertebral foramen, the
anterior and posterior roots unite to
 form a Trunk of spinal nerve Here,
the motor and sensory fibers become
mixed together, so that a spinal nerve
is made up of a mixture of motor and
sensory fibers .
 On emerging from the foramen, the
spinal nerve divides into 2 rami :
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B) Spinal Nerves
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1)Anterior ramus :
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it is a large mixed nerve .
The anterior ramus continues anteriorly to supply the
muscles and skin over the anterolateral body wall
and all the muscles and skin of the limbs.
It supplies those either directly or after plexuses
formation with neighbouring ventral rami .
The ventral rami are connected to the sympathetic
chain by rami communicantes
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B) Spinal Nerves
 2)posterior
ramus:
 It
is a smaller mixed nerve .
 The posterior ramus passes posteriorly
around the vertebral column to supply
the muscles and skin of the back.
 The dorsal rami do not form
plexuses
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The Somatic nerve plexuses:
The Somatic nerve plexuses:
 Most of the ventral rami of the spinal nerves have great tendency
to form nervous networks in which the nerve fibers exchanged
between the neighbouring ventral rami .
 At the root of the limbs, the anterior rami join one another to
form complicated nerve plexuses.
1- cervical
2-brachial plexuses: supply the skin &muscles of the upper limbs.
3- lumbar
4-sacral plexuses supply the skin &muscles of the lower limbs.
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N.B.: the 12 thoracic ventral rami do not form plexus .
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Functionally, the nervous system can be further divided into :
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the somatic nervous system, which controls
voluntary activities.
the autonomic nervous system, which controls
involuntary activities.
The nervous system, together with the
endocrine system, controls and integrates the
activities of the different parts of the body.
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SUMARY TO N.S
Central Nervous System
 The central nervous system is brain( cerebral hemisphere+
Brain stem cerebellum )+spinal cord composed of large numbers
of: a) nerve cells and
 b) their processes,
 c) supported by specialized tissue called neuroglia.
 the peripheral nervous system can be further divided into :
 a-the somatic nervous system, which controls voluntary
activities.
 a) 12 pairs of cranial nerves and
 b)31 pairs of spinal nerves and their associated ganglia.
 b- the autonomic nervous system, which controls involuntary
activities.
 The nervous system, together with the endocrine system,
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controls the activities of the different parts of body.
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2-Autonomic
Nervous
System
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2-Autonomic Nervous System
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2-Autonomic Nervous System
The autonomic nervous system is the part of the
nervous system concerned with the innervation
of involuntary structures such as: the heart,
smooth muscle , and glands throughout the
body .
It is distributed throughout the central and
peripheral nervous system.
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2-Autonomic Nervous System
The autonomic system
 divided into two parts
1)the sympathetic system .
2) the parasympathetic system.
 Both systems have antagonistic functions
but they are complementary to each other .
To control the muscles & glands,
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2-Autonomic Nervous System
The autonomic nervous system need 2 sets of
neurons :
 1 - preganglionic neurons : they carry the
impulses from the CNS to ganglia out side the CNS .
 2 - Postganglionic neurons : they carry impulses
from the ganglia to the smooth muscles and glands.
 A ganglia means a collection of neurons (cell bodies
) out side the CNS .
 .In the ganglia the pre & Postganglionic neurons meet by making
Synapse.
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1)the sympathetic system
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1.
The Functions of the sympathetic part of the autonomic
system:
prepare the body for an emergency,stress 3 f (fight
,freight,flight).
accelerates the heart rate,
causes constriction of the peripheral blood vessels, and raises the blood
pressure.
2.
3.
4.
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6.
Redistribution of the blood so that it leaves the areas of the skin
and intestine and becomes available to the brain, heart, and
skeletal muscle.
Dilatatios of the pupil.
Stimulation of sphincters of gut .
Erection of hairs .
sweating
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Sympathetic System
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: It is formed of :
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1) pre ganglionic fibers:
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Arise from neurons of the lateral horn of the
The gray matter of the spinal cord, in the
following segment :
1)all thoracic segment
2) the first and the second lumbar segment
,SO,the name thoraco lumber outflow
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the preganglionic fibers
The axons of these cells leave the spinal
cord in the
 anterior roots, nerve trunk ,ventral ramus
of the corresponding spinal nerve .
 Finally ,the preganglionic fibers leave the
ventral ramus as the white rami
communicantes to the ganglia of the
sympathetic chain.
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Once the preganglionic fibers reach the ganglia in the sympathetic
chain, they may pass to the following destinations by dividing into:
a- Ascending group: These are fibers W make synapses
with the cell bodies of upper ganglia of the chain.
b- Transverse group: These are fibers W make synapses
with the cell bodies of same level ganglia of the chain.
c- descending group: These are fibers W make
synapses with the cell bodies of lower ganglia of the
chain.
N.B.: SOME pre ganglionic fibers do not make synapse
with sympathetic chain ,Instead ,they reach other
distal sympathetic ganglia ,e.g., Coeliac ganglion where
they relay.
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2-The postganglionic nerve fibers
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The postganglionic nerve fibers: they are the axons of the
cell bodies of sympathetic ganglia .
They pass from the sympathetic ganglia to reach different
parts of the body by one of 3 methods :
1) by rejoining the ventral &dorsal rami to be distributed via
them.
The connection between the ganglia &ventral rami are called gray
rami communicantes .
They are distributed in the branches of the spinal nerves to supply
the smooth muscle in the walls of blood vessels, the sweat
glands, and the erector pili muscles of the skin.
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2)By passing along the blood vessels .
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3)By reaching the viscera directly.
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3) Sympathetic chains
1.
2.
3.
. Sympathetic trunks are two ganglionated nerve
trunks that extend the whole length of the vertebral
column
.There are 3 ganglia in each trunk of the neck, 11 or
12 ganglia in the thorax, 4 or 5 ganglia in the lumbar
region, and 4 or 5 ganglia in the pelvis.
The two trunks lie close to the vertebral column and
end below by joining together to form a single
ganglion, the ganglion impar.
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2) Parasympathetic System
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2) The
Functions of the Parasympathetic System
parasympathetic part of the autonomic system
conserving and restoring energy. i.e.,
rebuilding the body resources during rest :
1. They slow the heart rate
2. increase peristalsis of the intestine and glandular
activity, and open the sphincters.
3. constriction of the pupil.
NB .The hypothalamus of the brain controls the
autonomic nervous system and integrates the activities
of the autonomic and neuroendocrine systems, thus
preserving homeostasis in the body
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2) Parasympathetic System
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It is formed of:
1)The preganglionic fibers:
They arise from CNS in 2 sites :
1.
2.
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with the cranial nerves number 10,9,7,3.
From the neurons of the lateral horn of sacral
spinal segments number 2,3,4.
SO the name cranio -sacral outflow. leave the
spinal cord in the anterior roots of the
corresponding spinal nerves. They then leave
the sacral nerves and form the pelvic splanchnic63
2) Parasympathetic System
2 -peripheral ganglia:
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The preganglionic fibers synapse with cells in
peripheral ganglia, which are usually situated
close to the viscera they innervate.
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The cranial preganglionic fibers relay in (4 cranial
Para sympathetic ganglia )the ciliary,
pterygopalatine, submandibular, and otic ganglia .
The preganglionic fibers in the pelvic splanchnic
nerves relay in ganglia in the hypogastric
plexuses or in the walls of the viscera.
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3)The postganglionic fibers:
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The post ganglionic Para
sympathetic fibers (The axons
of the cell bodies inside the
ganglia ) leave the ganglia to
reach their targets.
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N.B.
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1) peripheral nerves can regenerate if
injured.
2) peripheral nerves are either :
a-Motor ( Efferent):if they carry orders ,e.g., to
a gland or muscle.
b-Sensory (Afferent) : if they carry sensations
,e.g., pain or touch.
c- Mixed: if they contain both motor &sensory
fibers .
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Clinical Notes
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Clinical Modification of the Activities of the
Autonomic Nervous System
Many drugs and surgical procedures that can modify
the activity of the autonomic nervous system are
available.
For example, drugs can be administered to lower the
blood pressure by blocking sympathetic nerve
endings and causing vasodilatation of peripheral blood
vessels.
In patients with severe arterial disease affecting the
main arteries of the lower limb.
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