What is the nervous system formed of ?
- Central nervous system (CNS) : includes the brain and the spinal cord.
- Peripheral nervous system ( PNS ) :
a. 12 pairs of cranial nerves and the sensory ganglia related.
b. 31 pairs of spinal nerves and the dorsal root ganglia. - Autonomic nervous system ( ANS ) : is formed of the sympathetic and parasympathetic systems ; ANS supplies smooth muscles , heart and glands.
What is the nerve cell ( neuron ) composed of ?
- The neuron is the anatomical , functional and embryological unit of the NS . It is formed of :
a. Cell body : it contains the nucleus.
b. Process : are two types : - The axon ( nerve fiber ) single , long process which carries nerve impulses away from the cell body. Outside the central nervous system , the axons run in groups to form the nerves.
- Dendrities : short , multiple processes which carry impulses towards the cell body.
Synapse : site where impulses pass from one neuron to another by contact of the axon of one neuron to the dendrites of the other ?
What is the composition of the CNS ?
Brain ( skull ) and spinal cord ( vertebral column ) are protected by bones , fluid ( cerebro-spinal fluid ) and meninges.
The meninges are :
1. pia mater ( a thin layer which is adherent to the brain )
2. Arachnoid ( has projections down to the pia mater ) and beneth it is the subarachnoid space through which the CSF is existent.
3. Dura mater ( a tough layer ) which is separated from the arachnoid mater by the subdural space.
What are the subdivisions of the brain ?
- Cerebrum : it contains two cerebral hemispheres and the diencephalon ( thalamus and hypothalamus ).
- Brain stem : it consists of mid brain , pons and medulla oblongata.
- Cerebellum : it consists of two cerebellar hemispheres.
What does the transverse section of the brain shows ?
- Grey matter ( outer ) : dark areas mainly on the surface of the cerebrum ( cerebral cortex ) . it contains cell bodies of the nerve cells.
- White ( inner ) matter : light areas in the center of the cerebrum( because it is surrounded by fat ). It contains axons ( nerve fibers ). The fibers run inside the CNS as bundles or tracts.
What is the spinal cord ?
It is the downward continuation of the medulla oblongata at the foramen magnum. it has a central narrow cavity called the central canal. It is divided into cervical , thoracic , lumbar , sacral and coccygeal.
What does the transverse section of the spinal cord show ?
- Outer layer of white matter : it contains the ascending fibers ( sensory tracts ) that carry sensations to the brain and descending fibers ( motor tracts ) that carry higher motor orders from the brain.
- Inner layer of grey matter : Contains neurons diposed in the form of H-shaped area. Two anterior horns ( motor ) and two posterior horns ( sensory ) of grey matter. The horizontal connecting region is known as the grey commissure , through which run the central canal . Lateral horn is present in thoracic and upper two lumbar segments , it is the only source of sympathetic fibers.
What are the cranial nerves ?
They are 12 pares :
- Olfactory
- Optical
- Occulomotor
- Trochlear
- Trigeminal
- Abducent
- Facial
- Vastibulo-cochlear
- Glossopharageneal
- Vagus
- Accesory
- Hypoglossal
What are the spinal nerves ?
They are 31 pairs :
8 cervical , 12 thoracic , 5 lumbar , 5 sacral , 1 coccygeal.
What is the structure of the spinal nerves ?
- Each spinal nerve is connected to the spinal cord by two roots : anterior ( ventral ) root which is carrying motor impulses away from the CNS and the posterior ( dorsal ) root which carries sensations towards the CNS.
- The anterior and posterior roots unite to form spinal nerve trunk ( mixed trunk )
- Once the spinal nerve emerges from the intervertebral foramen , it divides into a large anterior primary ramus and a small posterior primary ramus.
The posterior ramii are small , pass posteriorly to supply muscles and skin of the back and have to no tendency to firm plexuses.
The anterior ramii are larger , pass anteriorly to supply muscles and skin of the anterolateral body wall and all muscles and skin of the limbs and have tendency to form plexuses.
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