BYProf.Dr /

Olfat Anwar

The Nervous SystemIt controls and regulates all the body

functions.

It consisted of two parts:

I- Central Nervous System: consists of 2

structures:

A- the brain

B-the spinal cord.

II -Peripheral Nervous System

* Anatomically it consisted of the spinal

nerves and cranial nerves.

* Functionally it consisted of somatic

system and autonomic nervous system

A- The brain Its weight in adult is about 1,300 - 1,400

gm.

It is enclosed in the skull.

It is covered by three meninges (matter)

pia, arachinoid and dura .

The brain is formed by:

hemispheres cerebral ) The i

ii) Brain stem

iii) Cerebellum

i) The cerebral hemispheres

*Two cerebral hemispheres (C H) that are

connected by the corpus callosum.

Every cerebral hemisphere has many

elevations called sulci and in between

these sulci there are many depressions

called gyri .

The cerebral hemispheres consist of two

coats:

*Outer coat or the gray matter

containing the cell bodies.

* Inner coat or the white matter made

up of axons of the nerve cells which

form the tracts.

There are spaces filled with

cerebrospinal fluid (CSF) present in

between brain parts called ventricles .

Each half of the cerebrum is

further divided into four

different lobes:

Frontal lobe is the higher control

centre where consciousness lies

and is involved in problem

solving.

Parietal lobe perceives stimuli

such a somatosensory (touch) as

well as aiding speech s taste and

and reading.

Occipital lobe is devoted to the

most information intensive sense

of all, vision.

Temporal lobe controls hearing

and speech.

ii) Brain stem

Brain stem is formed of:

mid brain,

pons

and medulla oblongata.

These parts are responsible for basic vital

life functions such as breathing, heartbeat,

and blood pressure.

iii) Cerebellum

It has two hemispheres

and has a highly folded

surface or cortex.

Its function is regulation

and coordination of

movement, posture, and

balance.

B- The spinal cord

*Its length is 45 cm.

*It passes in the vertebral canal.

*It extends from the medulla oblongata and

ended at the level of the first or second

lumbar vertebrae.

*Its end called the cones medallaries.

*It is covered by three membranes; dura,

arachnoid and pia mater.

There are five (divisions) segments of the

spinal cord, corresponding to the vertebrae.

These segments give 31 pair of spinal nerves

II - Peripheral Nervous System

Anatomically it consisted of the spinal nerves

and cranial nerves.

Functionally it consisted of somatic system

and autonomic nervous system

A) The spinal nerves

There are 31 pair of spinal nerves in a human spinal cord:

Cervical nerves: (8 nerves in the neck) supply movement and feeling to

the arms, neck and upper trunk.

Thoracic (dorsal) nerves: (12 nerves in the upper back).

Lumbar nerves: (5 nerves in of the back of abdomen).

Sacral nerves: (5 nerves in the back of the pelvis).

Coccygeal nerve: (1 coccygeal nerves in the lower back).

Each spinal nerve is connected to the spinal cord by two roots .

Dorsal root (towards the back of the body)

Ventral root (from the front of the body).

The spinal nerves which are formed by the union of dorsal and ventral

roots are mixed nerves (motor and sensory).

The sensory carry information to the CNS, the motor carry information

away from the CNS.

B) Cranial nerves

There is 12 pair of cranial

nerves originated from the

brain.

The first and the second pair

emerge from the cerebrum.

The remaining 10 pairs emerge

from the brainstem.

All the cranial nerves

supplying only the head and

neck except the 10th nerve

(vagus nerve) which exceeds

and supply some thoracic and

abdominal organs.

Functioning classification of the peripheral nervous system:

*The Somatic System: it controls voluntary, skeletal, muscle

movement

*Autonomic Nervous System: it regulates involuntary,

subconscious activities such smooth muscle tone, the heart

rate and digestion. It further divided into the Sympathetic and

the Parasympathetic systems.

Sympathetic: It is called thoraco-

lumbar outflow.

The cell bodies of the sympathetic

preganglionic fibers pass within

the lateral horns of the spinal

segments T1-L2.

It prepares us for “fight or

flight”, because its stimulation

lead to increase heart rate, dilated

bronchial muscles, increased blood

pressure, and digestive slowdown.

Parasympathetic: It is called the cranio-sacral

outflow

a. The cranial part of the parasympathetic

nervous system: the long axons of neurons which

are present in the cranial nerves (III, VII, IX and

X).

b. The sacral part of the parasympathetic

nervous system: the myelinated axons of the

neurons in the gray matter of the 2nd, 3rd, 4th

sacral segments of the spinal cord

Parasympathetic nervous system is described as

“rest and digest”, which promotes energy

conservation such as a slower heart rate,

decreased blood pressure, and bronchial muscle

and urinary bladder constriction.

The Nerve Cell (Neurone)

It is the functioning and building unites of the CNS. Neurones are the cells which carry messages from one part of the body to another. It consists of:

Cell body: containing the nucleus. Its cytoplasm contains Nissls granules.

Axon: it is the longest one of these processes.

It is covered by myelin sheath which formed by the schwann cells. The myelin sheath has small gaps called Nodes of Ranvier.

It is responsible for carrying outgoing messages from the cell. On the end of the axon, the axon terminals (terminal buttons) are present.

The axon terminals can transmit information between cells

Terminal dendrites are smaller secondary processes that grow from the cell body

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