Nervous system The nervous system is divided into two parts : 1)The central nervous system . Consist the brain & the spinal cord . 2)The peripheral nervous system , consist 12 pairs of cranial nerves & 31 pairs of spinal nerves & associated ganglia . All this called somatic .

The autonomic N.S. which control involuntary activities are: 1) Sympathetic T1 to L 2-3 (Thoracolumber) . 2) Para sympathetic S 2-3-4 & Occulomotor, Facial , glossopharyngial , Vagus which is called (Craniosacrum ).

Central nervous system (CNS ) Large number of nerve cells & their processes , Supported by specialized tissue neuroglia . Neuron is the name given to the nerve cell & its Processes. The nerve cell have two type of processes called dendrites & an axon . The dendrites are short processes & the axon is the longest processes .

NEURON

The CNS organized into gray & white matter , gray matter consists of nerve cells embeded in neuroglia . White matter consists of nerve fibers ( axon ) Embeded in neuroglia .

Peripheral nervous system PNS Cranial nerves : They are 12 pair of cranial nerves that leave the brain & pass throw the foramina in the skull . All the nerves distributed in the head & neck Except the vagus which also supply structure in the thorax & abdomen .

SPINAL NERVE There are 31 pairs of spinal nerves that leave the Spinal cord & pass through the intervertebral Foramina in the vertebral column. The spinal nerves are named according to the region of the vertebral column with which they are associated : 8 cervical , 12 thoracic , 5 lumber , 5 sacral & 1 coccygeal

Each spinal nerve is connected to the spinal cord by two roots : The anterior (venteral ) root & the posterior (dorsal ) root . The anterior root is consist of bundles of nerve fibers carrying impulses away from the CNS called efferent fiber. Those efferent fibers that go to skeletal muscle & Cause them to contract called ( motor fibers ). Their cell of origin lie in the gray matter of the anterior horn of the spinal cord .

The posterior root consists of bundles of nerve fibers that carry impuls to the CNS & called afferent fibers. Concerned with sensation of touch , pain , temperature . They are called sensory fibers. The cell bodies of these nerve fibers in swelling on the posterior root called the posterior root ganglion .

At each the intervertebral foramen , the anterior & posterior root unite to form a spinal nerve . Motor & sensory fibers mixed together. Spinal nerve on emerging from the foramen Divides into : Large anterior ramus & small posterior ramus. The posterior ramus passes posteriorly to supply the muscl & skin of the back .

The anterior ramus continues anteriorly to supply muscle & skin of the limbs . Also the spinal nerve gives meningial branches to the meninges cover the spinal cord. The thoracic spinal nerves have branches rami communicates associated with sympathetic part of the autonomic N S .

plexus At the root of the limb , the anterior rami join one another to form complicated nerve plexuses . The cervical & brachial plexuses at the root of upper limb . The lumber & sacral plexuses at the root of lower limb.

Autonomic Nervous System Concerned with the innervation of involuntary structure such as the heart , smooth muscle & glands. The autonomic N S divided into two parts The sympathetic & the parasympathetic , they are regulate the action of viscera by balancing of their opposing action e.g. the sympathetic part accelerate the heart rate & raise blood pressure & decrease peristalsis of intestine.

The parasympathetic slow the heart rate , increase the peristalsisof intestine. Each ( sympathetic & parasympathetic) formed by two sets of neurons, the cell body of first set of neuron is located in the CNS, while the second set of neuron its cell body located out side of the CNS .

Sympathetic part ( thoracolumber) The gray matter of the spinal cord from the 1st thoracic segment to the 2nd lumber segment consist a lateral horn in this the cell body of the sympathetic neuron are located. .

Along the lateral aspect of the vertebral column there is achain of ganglia located oppisite most of the spinal nerves , connected with each other by nerve fibers to form sympathetic trunk .

The sympathetic trunk in the cervical region, three ganglia ( the superior, middle, & inferior cervical sympathetic ganglia ). In the thoracic region there are (10-11) ganglia . In the lumber there are( 3-4 ) ganglia . In the sacral ( 4-5 )ganglia.

The axones of the cells of the sympathetic neuron leave the spinal cord through the ventral ( anterior ) root of the spinal nerve as a preganglionic nerve fibers.

The preganglionic nerve fibers pass to the sympathetic trunk as a white ramus communicante . When the preganglionic nerve fibers reach the ganglia in the sympathetic trunk they may take one of the four courses:

1) It may synaps with neuron located in the ganglia & the fibers called post ganglionic fibers which leave ganglia to joins the coresponding spinal nerve through a gray ramus communicate & through the branchs of the spinal nerve it is distributed to supply the smooth muscle of the wall of the blood vessels, sweat glands of the skin ( in the head ).

2) Many of the preganglionic fibers also synaps with the neurons of the ganglia to form post ganglionic fibers which leave the ganglia & pass various visceral structure. e.g.some fibers pass with internal carotid artery & its branchs, these fibers called internal carotid plexus. (perivascular plexus) ( in the neck ).

3) After emerge from i.v.f. which form synaps with ganglia in the sympathetic trunk & go to organ ( in chest ) .e.g. cardiac plexus & pulmonary plexus .

4) After emerg from i.v.f. which not form synaps but go to ganglia in the abdomen called celiac ganglia & form synaps & go to organ in abdomen .

parasympathetic The glssopharyngeal n. go to otic ganglia & form synaps & carry fiber to parotid gland. Occulomotor n. carry fiber to ciliary ganglia & form synaps & go to lacrimal gl. Facial n. go to submandibular ganglia & form synaps & go to supply submandibular & sublingual salivary glands.

In the sacral segment Their neurons located in the gray matter of 2nd, 3rd, & 4th sacral segments of spinal cord. The preganglionic fibers leave the spinal cord in the anterior root of the corresponding sacral spinal nerves( 2nd, 3rd, 4th ) leave the nerves to inter the ganglia located near or within the wall of the organ to be innervated. The post ganglionic n. fibers leave the ganglia to innervate the organ.