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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