THE NERVOUS SYSTEM I. Description The nervous system is the body's information gatherer, storage center and control system. Its overall functions are to collect information about the body's external/internal states and transfer this information to the brain (afferent system), to analyze this information, and to send impulses out (efferent system) to initiate appropriate motor responses to meet the body's needs. The nervous system is a collection of cells, tissues, and organs. II. Function The Nervous System can be split into two separate divisions: the central nervous system and the peripheral nervous system. The central nervous system (CNS) acts as the command center of the body. It interprets incoming sensory information, then sends out instructions on how the body should react. The CNS consists of two major parts: the brain and the spinal cord. The peripheral nervous system (PNS) is the part of the nervous system outside of the CNS. It consists mainly of nerves that extend from the brain and spinal cord to areas in the rest of the body. Cranial nerves carry impulses to and from the brain while spinal nerves carry impulses to and from the spinal cord. The PNS can be divided into two systems: the somatic nervous system and the autonomic nervous system. The somatic nervous system controls the voluntary movements of the skeletal muscles. The autonomic nervous system control activities in the body that are involuntary or automatic. These include the actions of the heart, glands, and digestive organs and associated parts. The autonomic nervous system can be divided further into two subdivisions: the parasympathetic and sympathetic nervous systems. These two subdivisions work against each other. The parasympathetic nervous system regulates involuntary activities that keep the body running smoothly under normal, everyday conditions. The sympathetic nervous system controls involuntary activities that help the body respond to stressful situations.

III. Parts / Organ

NERVOUS SYSTEM: set of nerves, ganglions and nervous centers that receive sensory

signal. Commands and coordinates vital functions.

BRACHIAL PLEXUS: network of nerves of the arm.

INTERCOSTAL NERVE: cord conducting nerve impulses between the ribs.

RADIAL NERVE: cord conducting nerve impulses in the area of the radius.

MEDIAN NERVE: main cord conducting nerve impulses in the upper limb.

ULNAR NERVE: cord conducting nerve impulses in the area of the elbow.

LUMBAR PLEXUS: network of nerves of the lower back.

SCIATIC NERVE: cord conducting nerve impulses in the area of the thigh and lower

leg.

COMMON PERONEAL NERVE: cord conducting nerve impulses along the inside of the

lower leg.

SUPERFICIAL PERONEAL NERVE: cord conducting nerve impulses of the muscles

and skin of the leg.

DIGITAL NERVE: cord conducting nerve impulses of the fingers.

SACRAL PLEXUS: network of nerves of the sacrum.

SPINAL CORD: substance belonging to the nervous system, found in the holes of the

vertebrae.

CEREBELLUM: nervous centre situated under the brain.

CEREBRUM: seat of the mental capacities.

IV. Illness / Disease of the Nervous System Symptoms & Cure

ALZHEIMER DISEASE Alzheimer disease (AD) is the most common cause of dementia in western civilization. It affects more women than men, and the clinical course generally lasts approximately five years. The younger the individual is at the onset of the disease, the more severe the deficits for the patient. One famous contemporary who suffers from the disease is former U.S. President Ronald Reagan. Researchers continue to search for causes and cures for AD. The gene that codes for the B-amyloid protein located on chromosome 21 is implicated in the 20% of patients for whom there is a family history of AD. Head injury has been implicated in 3 to 5 % of AD cases. There is a 70 to 90% decrease in the production of the enzyme that makes acetylcholine. Other neurotransmitter abnormalities have also been implicated.

LOCKED-IN SYNDROME This syndrome is due to stroke, tumor or trauma to the ventral part of the rostral pons. Lesions there render the individual quadriplegic, unable to speak and incapable of facial movement. One would think these individuals were in a coma except that they are able to move their eyes and if given an eye communicating device they can communicate.

PARKINSON DISEASE Parkinson disease (PD) is characterized by a slowing of voluntary movements, bradykinesia, muscular rigidity and tremor at rest. These abnormalities result from a reduction of neurons that make dopamine in the pars compacta of the substantia nigra. The axons of these neurons normally release this neurotransmitter where they synapse, in parts of the basal ganglia called the caudate nucleus and putamen or, collectively, the corpus striatum. Dopamine usually works as an inhibitory neurotransmitter in the corpus striatum where it acts on cholinergic neurons. There are various causes for the loss of dopaminergic neurons in the substantia nigra and the resultant signs of PD. Some evidence exists for involvement of genetic factors in the pathogenesis of PD. For example, several large families with an autosomal, dominant inheritance pattern of PD have now been described, and the first genetic locus for PD has been identified in one of those families.

HUNTINGTON DISEASE This is an autosomally-inherited, dominant disorder in which the patient begins to exhibit symptoms in the third to fourth decades. Patients with Huntington Disease (HD) initially have a tendency to fidget which over months or years develops into jerky, choreiform movements. HD usually progresses over a 10 to 25 year period. As the disease progresses it leads to dementia and usually death from incurrent infection. There is a high incidence of suicide among patients with HD. Pathologically, there is atrophy of certain forebrain structures including the entire cerebral cortex and even more notably of the caudate nucleus and putamen The head of the caudate is reduced to a narrow brownish band of tissue that is flattened or concave. In normal brain the ratio of small neurons to large neurons in the corpus striatum is approximately 160:1 in Huntingtons patients the ratio is reduced to 40:1 with a marked decrease in the number of astrocytes. The gene for this disease has been isolated to the short arm of chromosome 4.

CEREBELLO-OLIVARY DEGENERATION OF HOLMES This is a rare, autosomally-inherited disease that leads to the progressive degeneration of the cerebellar cortex and the inferior olivary nucleus within the medulla. Onset is generally in the fourth decade. The disease results in ataxic gait, dysarthria, and tremor of the limbs. Autopsy reveals pronounced atrophy of the cerebellum. There is almost complete loss of Pukinje cells and an associated astrocytosis. Shrinkage is not as prominent in the olives. It is thought that the disease begins in the cerebellum and that in the inferior olivary nucleus the neuronal loss is secondary since the Purkinje cell is the synaptic target of the inferior olivary nucleus neurons. There is some similarity pathologically between this disease and chronic alcoholic degeneration in that both affect the cerebellum.

PITUITARY ADENOMA These tumors are benign and are usually composed of secretory cells from the anterior lobe of the pituitary. Initially the tumor results in either an increase or decrease of hormone production depending on whether or not the adenoma is composed of cells capable of producing hormone. Increased levels of hormones can lead to either Cushing disease or acromegaly. Secondary effects of tumor growth can lead to compression of the optic chiasm which has a position slightly above and in front of the pituitary gland. Such damage leads to visual difficulties.

WILSON DISEASE (Hepatolenticular Degeneration) This disease is caused by the inheritance of a mutation on chromosome 13. The mutation prevents the body from eliminating excess copper. Ceruloplasmin is the protein that binds and removes excess copper and its levels are greatly reduced in this disorder. Too much copper in the system damages the cells of the liver and leads to cirrhosis. Neurological damage primarily occurs in the putamen and globus pallidus, collectively known as the lenticular nucleus. The disease first affects the liver, and if treatment is administered early enough, damage to the nervous system is dramatically reduced. Treatment includes the elimination of copper containing foods such as chocolate and mushrooms. Patients are also given drugs to chelate excess copper and eliminate it from the body.

WERNICKE-KORSAKOFF SYNDROME This disease, notably frequent among chronic alcoholics, is due to a deficiency of vitamin B1 or thiamine. The poor diet of alcoholics who are suffering from this syndrome leads to lesions and increased microhemorrhages in the mammillary bodies, thalamus and brainstem. This syndrome can also be associated with diseases of the GI tract when there is inadequate thiamine absorption. Neurologic symptoms include confusion, memory loss, impaired movements and peripheral neuropathy. Immediate administration of thiamine is usually successful in treating the symptoms, but sometimes permanent memory loss occurs.