The nervous system is a very complex system in the body. It has many, many parts. The nervous system is divided into two main systems, the central nervous system (CNS) and the peripheral nervous system. The spinal cord and the brain make up the CNS. Its main job is to get the information from the body and send out instructions. The peripheral nervous system is made up of all of the nerves and the wiring. This system sends the messages from the brain to the rest of the body.
The human nervous system represents the product of millions of years of evolution, particularly in the degree of encephalization or brain complexity. It can be divided into central and peripheral parts for descriptive purposes, although there is both anatomical and functional continuity between the two parts.
The central nervous system consists of the brain and the spinal cord. The peripheral nervous system is not so clearly subdivided, but its anatomical parts are: (1) the spinal nerves; (2) the cranial nerves; and (3) the autonomic nervous system.
Thirty-one pairs of spinal nerves originate from the spinal cord. They are all mixed nerves, and they provide a two-way communication system between the spinal cord and parts of the arms, legs, neck and trunk of the body. Although spinal nerves do not have individual names, they are grouped according to the level from which they stem, and each nerve is numbered in sequence. Hence, there are eight pairs of "cervical nerves" (numbered C1 - C8), twelve pairs of "thoracic nerves" (T1 - T12), five pairs of "lumbar nerves" (L1 - L5), five pairs of "sacral nerves" (S1 - S5), and one pair of "coccygeal nerves". The nerves coming from the upper part of the spinal cord pass outward nearly horizontally, while those from the lower regions descend at sharp angles. This is derived from the consequence of growth. In early life, the spinal cord extends the entire length of the vertebral column, but with age, the column grows faster than the cord. As a result, the adult spinal cord ends at the level between the first and second lumbar vertebrae, so the lumbar, sacral, and coccygeal nerves descend to their exits beyond the end of the cord.
The brain is a jelly-like substance, which in adults weighs about three pounds. It is divided into three parts: the brain stem, which is an extension of the spinal cord, the forebrain (which consists mainly of the cerebruim) and the cerebellum. The forebrain and cerebellum are divided into two hemispheres which are linked by a thick band of nerve fibers and these hemispheres have areas, called "lobes," which perform specific functions. The brain's surface lies in rather ugly, wrinkled folds. Traditionally referred to as one's "gray matter," it does, indeed, contain gray nerve cell bodies which surround a smaller mass of white nerve fibers. The brain, like the heart, is protected by a buffer zone. This, in the form of fluid, may be the source of "water on the brain," but it is very necessary to our survival. Only these pools of fluid and the skull protect the brain from the bumps and grinds of daily living which would damage this fragile organ. With them, we are able to think, reason, love, forgive, create and remember, as well as to survive through automatic processes such as breathing and digesting, and we have reflexes which signal in case of "fight or flight" emergencies. Just think of it!
The facial nerve is the seventh cranial nerve. It begins in parts of the brain stem and branches into the face, neck, salivary glands and outer ear. The facial nerve performs both motor and sensory functions. Branching up from the brain stem, it divides into smaller nerves that reach into the face, neck, salivary glands and the outer ear. These branches control the muscles of the neck, the facial expressions, and the muscles of the forehead. They also stimulate secretions of the lower jaw and those salivary glands which are in the front of the mouth. Along with this, they report taste sensations from the front two-thirds of the tongue and carry sensations from the outer ear. Although a spontaneous grin and a deliberate smile both use lip and cheek muscles, each involves a different neural pathway from the brain.
Femoral nerves are branches which stem from the lumbar nerves and divide into many smaller branches to supply motor impulses to the muscles of the thighs and legs; they receive sensory impulses from the skin of the thighs and the lower legs.
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