NERVOUS SYSTEM
The major divisions of the human nervous
system are
(a) Central nervous system (CNS),
(b) Peripheral nervous system (PNS)
• The central nervous system consists of the brain
and spinal cord
• The peripheral nervous system consists of nerve
fibers (cranial and spinal nerves) and cell bodies
outside the CNS
Major Subdivisions of the CNS
• Brain
• Spinal cord
THE HUMAN BRAIN
• The human brain has three major
subdivisions:
(1) Brainstem
(2) Cerebellum
(3) Cerebrum
The cerebellum .
A :Superior
view .B :Inferior
view
The Brain stem
• Midbrain
• Pons
• Medulla oblongata
THE SPINAL CORD
The spinal cord is the
continuation of the medulla
oblonagata. It is enclosed by
meninges inside the upper
part of the vertebral canal. It
is divided into 31 segments:
8
Cervical segments
12
Thoracic segments
5
Lumber segments
5
Sacral segments
1
Coccygeal segment
Spinal nerves
• A nerve is a bundle of neuron processes which
carry impulses to and from the CNS. Those
nerves arising from the spinal cord are spinal
nerves. There are 31 pairs of spinal nerves.
Cross Section of the Spinal Cord
The peripheral nervous system
• Categories of PNS Nerves
(1) Cranial nerves
(2) Spinal nerves
Cranial nerves
• The 12 pairs of nerves attached to the right
and left sides of the brain are called cranial
nerves.
• Each cranial nerve is identified by a Roman
numeral in order from I to XII and an
individual name. For example, the Vth ("fifth")
cranial nerve is known as the trigeminal nerve.
Cranial nerves:
1-The first (I) is the olfactory nerve. It is purely
sensory and carries the smell sensation from the
nose.
2-The second (II) is the optic. It is purely sensory and
carries the vision from the eye.
3-The third (II) is the oculomotor nerve. It is motor to
some muscles of the eye. It has parasympathetic
fibers which constricts the pupil.
4-The fourth (IV) is the trochlear nerve. It is purely
motor. It supplies a single muscle of the eye.
5- The fifth (V) is the trigeminal nerve. It is divided into three
branches; Ophthalmic, maxillary, and mandibular
6- The sixth (VI) is the abducent nerve. It is purely motor
and supplies one muscle in the eye.
7- The seventh (VII) is the facial nerve. It is a mixed nerve. It is
motor to muscles of the face and carries taste sensation
from the anterior two thirds of the tongue. It has
parasympathetic secretory fibers to the lacrimal,
submandibular and sublingual salivary glands.
8- The eight (VIII) is the vestibulocochlear nerve. It is purely
sensory. It carries the hearing sensation and senses of
equilibrium.
9- The ninth (IX) is the glossopharyngeal nerve. It
carries the taste sensation from the posterior 1/3 of
the tongue. It is also motor to some muscles in the
pharynx. It has parasympathelic fibers to the parotid
gland.
10- The tenth (X), is the vagus nerve, and is motor to
smooth muscles of the gastrointestinal tract and
respiratory muscles. It carries parasympathetic
inhibitory fibers to the heart.
11- The eleventh (XI) is the accessory nerve. It assists
the vagus nerve in supplying muscles of pharynx and
larynx.
12- The twelfth (XII), is the hypoglossal nerve, is
motor to the muscles of the tongue.
Spinal nerves
• Attached to the sides of the spinal cord are 31
pairs of spinal nerves.
• The spinal nerves are named by:
(a) The region of the spinal cord with which the
nerve is associated.
(b) An Arabic numeral within the region. For
example, T-5 is the fifth spinal nerve in the
thoracic region.
A "TYPICAL" SPINAL NERVE
The autonomic nervous system (ANS)
• a) The sympathetic system:
•
It is connected centrally to the spinal cord
segments from the first thoracic to the third
lumbar (thoraco-lumbar).It prepares the body
for emergency.
• b) The parasympathetic system: It is divided into
(cranio-sacral):
• 1- Cranial part in the cranial nerves 3, 7, 9, 10.
• 2- The sacral part which is connected centrally
with the sacral segments 2, 3 and 4 of the spinal
cord.
• Activities of the parasympathetic system aim at
conserving and restoring energy of the body.
The meninges:
These are the coverings of the brain and spinal cord. It
is formed of three layer :
1The pia matter which is attached to the brain and
spinal cord.
2The arachnoid matter (the middle layer).
3The dura matter (the outer fibrous layer).
The meninges protect the brain and spinal cord.
The subarachnoid space contains blood vessels that
supply the brain and spinal cord as well as a watery fluid
known as the cerebrospinal fluid C.S.F. which circulates
inside the brain cavities (ventricles) and the central canal
of the spinal cord.