- 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