Nerves

Question 1

What is the nervous system formed of ?

Answer 1

1. Central nervous system (CNS) : includes the brain and the spinal cord.
2. 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.
3. Autonomic nervous system ( ANS ) : is formed of the sympathetic and parasympathetic systems ; ANS supplies smooth muscles , heart and glands.

Question 2

What is the nerve cell ( neuron ) composed of ?

Answer 2

1. 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 :
2. 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.
3. 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 ?

Question 3

What is the composition of the CNS ?

Answer 3

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.

Question 4

What are the subdivisions of the brain ?

Answer 4

1. Cerebrum : it contains two cerebral hemispheres and the diencephalon ( thalamus and hypothalamus ).
2. Brain stem : it consists of mid brain , pons and medulla oblongata.
3. Cerebellum : it consists of two cerebellar hemispheres.

Question 5

What does the transverse section of the brain shows ?

Answer 5

1. Grey matter ( outer ) : dark areas mainly on the surface of the cerebrum ( cerebral cortex ) . it contains cell bodies of the nerve cells.
2. 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.

Question 6

What is the spinal cord ?

Answer 6

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.

Question 7

What does the transverse section of the spinal cord show ?

Answer 7

1. 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.
2. 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.

Question 8

What are the cranial nerves ?

Answer 8

They are 12 pares :

1. Olfactory
2. Optical
3. Occulomotor
4. Trochlear
5. Trigeminal
6. Abducent
7. Facial
8. Vastibulo-cochlear
9. Glossopharageneal
10. Vagus
11. Accesory
12. Hypoglossal

Question 9

What are the spinal nerves ?

Answer 9

They are 31 pairs :

8 cervical , 12 thoracic , 5 lumbar , 5 sacral , 1 coccygeal.

Question 10

What is the structure of the spinal nerves ?

Answer 10

1. 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.
2. The anterior and posterior roots unite to form spinal nerve trunk ( mixed trunk )
3. 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.

Question 11

https://www.youtube.com/watch?v=XEFumtI-pSk

Answer 11

https://www.youtube.com/watch?v=Qh6A1neljbI