FREE ESSAY ON NERVOUS SYSTEM

NERVOUS SYSTEM

The Nervous system 
The nervous system can be separated into three divisions, the central nervous system, the
peripheral nervous system, and the autonomic nervous system. The Central Nervous system
consists of the brain and the spinal cord. The spinal cord is a long, thick nerve trunk
that rus from the base of the brain down through the spinal column, or backbone. The cord
is composed of white matter. A cross sectional view of the spinal cord shows the gray
matter as an H shaped area surrounded by white matter. Thirty one pair of spinal nerves
leave the spinal cord. Each of these nerve trunks is attacked to the cord in two places.
The root of the nerve that leaves the cord toward the from to fight body is called the
ventral root or anterior root. The root that leaves toward the rear of the body is called
dorsal root or posterior root. Sensory nerves enter the spinal cord at the dorsal root.
Motor nerves leave the spinal cord at the ventral root. If the ventral root of a nerve is
cut, the part of the vody to which the nerve goes cannot move, but it still has
sensation. If the dorsal root of a nerve is cut, sensation disappears, but the body part
can still move. Some nerve impulses entering the spinal cord are directed to the brain. 
The Peripheral Nervous system consists of 12 pairs of cranial nerves and the 31 pair of
spinal nerves. The Cranial Nerves come from the lower part of the brain. These neves
control many sensations and actions including sight, smell, chewing, and swallowing. The
spinal nerves leave the spinal cord at the small of the back. Each of the 5 pair of
sacral nerves and the 1 pair of coccygeal nerves leave the spinal cord between the lowest
vertebrae in the spinal cord.
The autonomic Nervous system regulates the inernal organs of the body. The fuctions it
controls are involuntary. For example, you cannot deliberately control the rate of your
heartbeat, though it may be influenced by your thoughts or emotions.
The nerves of the autonomic nervous system are connected to and regulated by the central
nervous system are connected to and regulated by the central nervous sytem at a
subconscious level. The nerve fibers have lettle or no myelin sheath. Most nerves in the
autonomic system are effector speed of more than 300 per second. In the smaller fibers of
the autonomic nervous system, the lowerst part of the brain. The membrane theory is the
most commonly accepted theory of how 
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