NERVOUS SYSTEM

- the nervous system is the body’s fast pacing control system. It consist of the brain, spinal cord, nerves, and sensory receptors, the body must be able to respond to irritants or stimuli coming from the outside of the body (such as light, sound, or changes in temperature) and from inside the body (such as decreases in oxygen or stretching of tissue). The sensory receptors detects changes and send messages (via electrical signal called nerve impulses) to the central nervous system (brain and spinal cord) so that is constantly informed about what is going on. The central nervous system then assesses this information and responds by activating the appropriate body effectors (muscles or glands).

BRAIN- a very clever or intelligent person is often spoken of as a “brainy” individual. This expression suggest that reasoning, remembering, learning and thinking ahead are in some way centered in a person’s brain. This is true. However, the brain is also concerned with activities other than these higher processes. It is involved in some way with everything that happens in or to a person’s body.  Man is able to see, hear, taste, and touch because his brain receives sensory impulses and make him respond to them. The brain coordinates the physical activities involved in talking, walking, running, or lifting. It is also plays a role in vital processes such as respiration, circulation, and digestion.

The brain may be described as the master control mechanism of the body’s vast and complex communication network-the nervous system. To better understand the brain, one should first know something about nerves. These are the structures which carry sensory and motor impulses between the brain and other body parts.

NERVES­- nerves course throughout the body in much the same way that railroad lines cross a country. The brain can be considered as a complicated but orderly switchyard. Some nerves bring impulses to the brain from body parts such as the skin, joints, muscles and sense organs. These are the sensory nerves. Others, the motor nerves, transmit impulses from the brain to the muscles, such motor impulses cause the muscles to contract. Thus all bodily movements are controlled by motor nerve impulses. The organ and system of organ which carry out vital processes such as respiration, circulation, and digestion are regulated by autonomic nerves.

SPINAL CORD- most nerves connect with a cable like structures, the spinal cord. It routes their impulses to or from the brain, it runs through a tunnel of bone, the vertebral column, or backbone, and is thus well protected. The spinal cord is made up of many tightly bound nerves fibers. These fibers extend the length of the cord. Specific groups of them are bundled together to form special pathways. Such as bundles of nerve fibers are called nerve tract

NERVE TRACT IN THE SPINAL CORD- when a sensory nerve enters the spinal cord, it joints its special nerve tract. This tract carries its impulses to the brain. It is called a sensory nerve tract. It is also known as an ascending nerve tract, because it carries impulses “upward” or to the brain. Other nerve tracts carry impulses from the brain. These are the motor nerve tracts. Because they transmit impulses “downward,” or away from the brain, they are also called descending tracts. At a point just above the neck region the spinal cord thickens. This marks the area where the cord merges with the brain. Here fibers from each ascending tract fan out from the cord and end in special collections of cells called sensory nerve centers. The general function of such a center is to receive and redirect the specific sensory impulses. Other nerve centers are the areas of origin, rather than the ends, of certain nerve tract. These are the motor nerve centers. They give rise to the motor nerve tracts. Instead of fanning out, as a sensory fibers do when they leave the cord and enter the brain, the motor nerve tract converge when they reach their point of entry from the brain into spinal cord.

PREPARED BY: JULLENA V. DE LEON