�ݺ�ߣ

Anatomical divisions of the
nervous system:
 A) Central nervous system (CNS):
 1- Brain :
 a) Cerebrum.
 b) Cerebellum.
 c) Brain stem.
 2- Spinal cord (31 segments).

 B) Peripheral nervous system:
 This consists of the peripheral nerves that
arise from the central nervous system, and
they include:
 1- The cranial nerves.
 2- The spinal nerves.
 3- The autonomic nerves:
 a) Sympathetic nerves.
 b) Parasympathetic nerves.

autonoddddddddddddddddddddddddmic 1 .ppt

1-The sympathetic nervous
system:
This arises from the lateral horn
cells (LHCs) of all thoracic and
upper 3 lumbar segments of the
spinal cord (thoracolumbar
outflow).

 2-The parasympathetic nervous
system:
 This arises from LHCs of the 2nd, 3rd and 4th
sacral segments of the spinal cord as well as
from the nuclei of certain cranial nerves, which
include:
 a) The 3rd cranial nerve (oculomotor).
 b) The 7th cranial nerve (facial).
 c) The 9th cranial nerve (glossopharyngeal).
 d) The 10th cranial nerve (vagus).

Reflex action:
 It is an involuntary response to a stimulus.
 It is the functional unit of the nervous
system.
 1- Somatic reflex actions: regulate the
activity of skeletal muscles.
 2- Autonomic reflex actions: regulate the
activity of the viscera.

Autonomic ganglia
 Autonomic ganglion is a collection of
nerve cells outside the C.N.S.
 It contains the postganglionic neurons.
 Preganglionic fibers may pass through
several autonomic ganglia but it relays
only in one ganglion.

Types of autonomic ganglia:
 1- Lateral (paravertebral) ganglia:
These ganglia are the main sites for relay
of preganglionic sympathetic fibers.
 2- Collateral (prevertebral) ganglia:
These are present mainly in the abdomen
in close relation to the aorta. These ganglia
are sympathetic.

3-Terminal ganglia:
These are present near or in the
walls of the effector organs.
These ganglia are mostly the
sites for relay of preganglionic
parasympathetic fibers.

Functions of autonomic ganglia:
Distributing centre: the preganglionic
fibers arise from limited regions of brain
stem and spinal cord. By the aid of
autonomic ganglia, each preganglionic
fiber diverges to average 8-9 postganglionic
neurons.

The sympathetic nervous
system
 The sympathetic nervous system can
be divided into 4 divisions:
 1- Cervical.
 2- Cardio-pulmonary.
 3- Splanchnic.
 4- Somatic.

1-Cervical division
 This division supplies different
structures in the region of the head and
neck.
 a) Origin: preganglionic fibers arise
from the lateral horn cells (L.H.Cs) of
the upper 2 thoracic segments.
 b) Relay: in the superior cervical
sympathetic ganglion.

c)Functions:
1-Eye:
 a) Contraction of the dilator pupillae muscle
leading to pupil dilatation (mydriasis).
 b) Contraction of muscles in the eyelids
(called superior and inferior tarsal muscles)
→ lid retraction→ widening of the palpebral
fissure.

 c) Contraction of Muller's muscle
behind the eyeballs → exophthalmos.
 d) Vasoconstriction (VC) of the blood
vessels of the eye.
 e) Relaxation of the ciliary muscle
during far vision.

2-Salivary glands:
 a) Trophic secretion (small in volume,
viscous and rich in organic material).
 b) Motor to the myoepithelial cells
surrounding the acini → squeeze saliva.
 c) Vasoconstriction of the salivary blood
vessels.

3- Skin:
 a) Vasoconstriction of the cutaneous blood
vessels.
 b) Sweat secretion.
 c) Hair erection as a result of contraction of
certain muscles in the skin called pilomotor
muscles.
 4- Brain:
 Slight vasoconstriction to the cerebral blood
vessels.

Horner's syndrome
 An injury to the cervical sympathetic
nerve fibers produces a syndrome
(group of symptoms) on the same side
called Horner's syndrome.
 The symptoms of Horner's syndrome:
 1- Ptosis: drooping of the upper eyelid
due to paralysis of the superior tarsal
muscle.

 2- Miosis (pupilloconstriction) due to
paralysis of the dilator pupillae muscle.
 3-Anhydrosis (absence of sweat secretion).
 4-Vasodilatation (VD) due to loss of
sympathetic V.C effect, so it becomes warmer
and more red than the healthy side.
 5- Enophthalmos (sinking of the eyeball
backward in the orbit) due to paralysis of
Muller's muscle.

2-Cardiopulmonary division
 This division supplies the heart and
lungs.
a) Origin: preganglionic fibers
arise from L.H.Cs of the upper 4
thoracic segments.
b) Relay: in the cervical and upper
4 thoracic lateral ganglia.

c) Functions:
1-heart:
 a) Stimulates all properties of the cardiac
muscle.
 b) Vasodilatation of the coronary vessels
(indirect effect).
 c) Increases the O2 consumption of the
heart.

2-Lungs:
a) Inhibits mucus secretion of
bronchial glands.
b) Produces bronchodilatation.
c) V.C of the pulmonary vessels.

3- Splanchnic (visceral) division
 This division supplies different abdominal
and pelvic viscera.
 a) Sympathetic supply to the abdomen
(greater splanchnic nerve):
 Origin: preganglionic fibers arise from the
L.H.Cs of the lower 6 thoracic segments.
 Relay: in the collateral ganglia in the
abdomen.

Functions:
 1- V.C of the majority of the arterioles in the
stomach, small intestine, proximal part of the
large intestine, kidney, liver and pancreas.
 2- Relaxation of the walls of the stomach,
small intestine and proximal part of the large
intestine and contraction their corresponding
sphincters.

 3- Contraction of the smooth muscle in the
capsule of spleen→ squeeze the stored blood
into circulation.
 4- Stimulation of glycogenolsis in the liver→
increased blood glucose level.
 5- Stimulation of adrenal medulla to secrete its
hormones (catecholamine).
 6- Inhibits insulin hormone secretion.

b)Sympathetic supply to the
pelvis (lesser splanchnic nerve):
Origin: preganglionic fibers arise
from the L.H.Cs of the upper 3 lumber
segments.
Relay: in the collateral ganglia in the
abdomen.

Functions:
 1- Relaxation of the urinary bladder
wall and contraction of the internal
urethral sphincter→ urine retention.
 2- Relaxation of the walls of the rectum
and distal part of the large intestine and
contraction of the internal anal
sphincter→ retention of feces.

 V.C of blood vessels in the pelvic viscera and
erectile tissues → inhibition of erection and
shrinkage of these organs.
 4- In the male, it causes contraction of the
smooth muscle in the vas deferens, seminal
vesicles and prostate→ ejaculation of semen.
 5- In the females, it produces variable effects
on the uterus (contraction or relaxation)
depending on …………….

4-Somatic division
 This division of the sympathetic nervous system
accompanies the somatic nerves and supplies
with them the skin and skeletal muscles.
 a) Sympathetic supply to the upper limbs:
 Origin: preganglionic fibers arise from LHCs of
the thoracic 4-8 segments.
 Relay: in the cervical and upper 4 thoracic
ganglia.

Functions:
1- Skin: V.C, sweat secretion and
erection of hair.
2- Skeletal muscles:
 a) V.D of skeletal muscles blood vessels.
 b) Stronger contraction, delayed fatigue
and rapid recovery (Orbelli effect).

 a) Sympathetic supply to the lower
limbs:
 Origin: preganglionic fibers arise from
LHCs of the thoracic 10 - 12 segments and
lumber 1-2 segments.
 Relay: in the lumber and sacral ganglia.
Functions:
 The same as in the upper limbs.

�ݺ�ߣ

autonoddddddddddddddddddddddddmic 1 .ppt

More Related Content

autonoddddddddddddddddddddddddmic 1 .ppt