Download 04 - nervous system

NERVOUS SYSTEM
It is the master 
controlling and
communicating
system of the body.
Structurally, it has 
two subdivisions :
(1) Central nervous
system.
(2) Peripheral 
nervous system.

NERVOUS SYSTEM
Functionally, it is divided into : 
Somatic N.S. : It controls voluntary
activities.
Autonomic N.S. :It controls 
involuntary activities.

CENTRAL NERVOUS SYSTEM
It is composed of 
the brain and
spinal cord.
They occupy the 
dorsal body cavity.
They act as the 
integrating and
command centers
of the nervous
system.
CENTRAL NERVOUS SYSTEM
Its interior is 
organized into
Gray and White
matter.
CENTRAL NERVOUS SYSTEM
Gray matter: 
Consists of nerve cells 
(neurons) embedded in
neuroglia.
Each neuron has two 
types of nerve
processes:
Dendrites : short 
processes of the cell
body.
Axon : longest process 
of the cell body.
CENTRAL NERVOUS SYSTEM
White matter: 
Consists of nerve
fibers embedded
in neuroglia.

PERIPHERAL NERVOUS
SYSTEM
It is the part of the 
nervous system
outside the CNS.
It consists of (12) 
pair cranial and (31)
pair of spinal
nerves.
These nerves act as 
communication lines
between all parts of
the body and the CNS.
PERIPHERAL NERVOUS
SYSTEM
The nerves are 
formed of grayish
white cords.
Each cord is 
formed of nerve
fibers (axons)
supported by
delicate areolar
tissue.
CRANIAL NERVES
The twelve pair of
nerves supply
structures in the
head and neck.
The 10th (vagus)
supplies structures
in the thorax and
abdomen.


SPINAL NERVES
They are named 
according to the region of
the spinal cord to which
they are associated.
They are: 8)cervical. 
12)thoracic. 5)lumbar.
5)sacral and 
(1) coccygeal. 
LENGTH OF SPINAL NERVES
In the upper 
cervical region,
they are short and
horizontal.
The lumbar and 
sacral nerves
below the level of
termination, form a
vertical bundle
(Cauda Equina).
LEVEL OF TERMINATION OF
S.C.
Adults : 
It terminates inferiorly at
the lower border of the
1st lumbar vertebra.
Children : 
It is relatively longer and
ends at the upper border
of the third lumbar
vertebra.


SPINAL NERVES
Each spinal nerve
is attached to the
spinal cord by two
roots : Anterior
and Posterior.

ANTERIOR ROOT
It carries nerve impulses
away from the central
nervous system
(Efferent) fibers.
The efferent fibers to 
the skeletal muscles are
called (Motor) fibers.
They arise from the 
anterior gray horn cells
of the spinal cord

POSTERIOR ROOT
It carries impulses to the 
central nervous system
(Afferent) fibers.
It conveys sensations of 
pain, touch and
temperature (Sensory)
fibers.
Their cell bodies are 
located in the posterior
root ganglion.
SPINAL NERVE
At the intervertebral 
foramen the anterior
and posterior roots
unite to form a spinal
nerve.
Each spinal nerve is a 
mixture of motor and
sensory fibers.
FORMATION OF THE RAMI
On emerging from
the foramen, each
spinal nerve
divides into a large
ventral (anterior)
ramus and a
smaller dorsal
(posterior) ramus.

DISTRIBUTION OF THE RAMI
The posterior rami 
pass posteriorly to
supply the skin and
muscles of the back.
The anterior rami 
supply the skin and
muscles of the limbs
and the anterolateral
wall of the body.
PLEXUSES
At the root of the 
upper limb, the
anterior rami
unite to form the
Cervical and
Brachial plexuses.
At the root of the 
lower limb, they
form the Lumbar
and Sacral
plexuses.
AUTONOMIC NERVOUS SYSTEM
It is concerned with 
the innervation of the
involuntary structures
(heart, smooth
muscles ,glands).
It is divided into : 
AUTONOMIC NERVOUS SYSTEM
1. Sympathetic 
system: it prepares the
body for an emergency.
2. Parasympathetic 
system :
It conserves and restores
energy.
Each system has : 
Efferent, Afferent fibers 
and ganglia to relay.

SYMPATHETIC SYSTEM
Efferent fibers : 
Their cell bodies 
are located in the
lateral column of
the spinal cord
from the level of
(T1- L2).
They are divided 
into :
SYMPATHETIC SYSTEM
A. preganglionic fibers 
They leave the lateral column
of the spinal cord in the
anterior nerve roots.
They pass in the White rami
communicantes to the
paravertebral ganglia of
the sympathetic trunk.


SYMPATHETIC TRUNKS
They are two ganglionated 
trunks that extend close to the
vertebral column.
Each trunk is formed of (3) 
ganglia in the neck, (12) in the
thorax, (5) in the lumbar and
(5) in the sacral.
The two trunks end inferiorly by
forming one ganglion.
Ganglion : collection of nerve
cells (neurons) outside the
central nervous system.


PREGANGLIONIC FIBERS
1. They relay at the 
corresponding ganglia
by synapsing with an
excitor cell of the
ganglion.
2. Fibers in the upper 
thorax may travel up in
the sympathetic trunk to
relay in the cervical
ganglia.
PREGANGLIONIC FIBERS
3. Splanchnic nerves 
They pass through the 
thoracic sympathetic
ganglia without relay.
They pass through the 
diaphragm.
They are : 
a. Greater Splanchnic 
nerve (5th -9th ) thoracic
ganglia.
It relays in the celiac 
ganglia.
PREGANGLIONIC FIBERS
b. Lesser splanchnic 
nerve (10th & 11th )
ganglia :it synapses with
ganglia in the lower part
of the celiac trunk.
C. Least splanchnic 
nerve (12th) ganglion :
It relays in ganglia of the
renal plexus.


POSTGANGLIONIC FIBERS
They pass through
the Gray rami
communicantes
to join the spinal
nerves to supply
the smooth
muscles in the
blood vessels,
sweat glands and
erector pili muscles
of the skin.

POSTGANGLIONIC FIBERS
The postganglionic
fibers of the
splanchnic nerves
supply the smooth
muscle and glands
of the viscera.

AFFERENT FIBERS
They arise from the wall of 
the viscera.
They pass through the 
sympathetic ganglia
without relay.
They enter the spinal nerve 
through the white rami.
They relay in the posterior 
root ganglion of the
corresponding spinal nerve.
Their central axons pass to 
the spinal cord.
PARASYMPATHETIC SYSTEM
Efferent fibers 
(Preganglionic) :
(1) Cranial part : 
Their cells are 
located in the
brain.
They form part of 
the cranial
nerves (111,
V11,1X &X).
PARASYMPATHETIC GANGLIA
They relay into 
ganglia situated close
to the tructures they
supply.
In the head & neck, 
they are the (ciliary,
otic, pterygopalatine
and submandibular)
ganglia.
PARASYMPATHETIC SYSTEM
(2) Sacral part : 
The fibers arise from
the gray matter of
the 2nd,3rd and 4th
sacral spinal
segments.
They form the Pelvic
splanchnic nerves.
They relay in ganglia
in the walls of the
viscera or in the
hypogastric plexuses.



PARASYMPATHETIC SYSTEM
Afferent fibers : 
They pass from the 
viscera to the
sensory ganglia of
the cranial nerves or
the posterior root
ganglia of the
sacrospinal nerves.
The central axons 
pass to the central
nervous system.