The Brain

The brain is the master organ of the body. From our eyes,
ears, nose, and skin, the brain receives messages that tell
us what is going on in the world about us. The brain also
receives a steady stream of signals from other body organs
that enables it to control the life processes. 

The brain stores information from past experiences. This is
why we can learn, remember, and think. The brain selects
and combines messages from the senses with memories and
emotions to form various thoughts and reactions. 

The brain is a greatly expanded bulb at the upper end of
the spinal cord. It consists mainly of neurons, or nerve
cells; supporting cells, and blood vessels. The nerve cells
carry out the brain's functions. Each of the billions of
tiny neurons consists of a cell body and a number of
fibers. These fibers connect the cell body with other cell
bodies. The brain is not a single organ; it has many parts
with special functions, though they are all connected.
Messages to the brain all pass through the brain stem. From
the brain stem, they go to different parts of the brain for
'processing.' Messages go out through the grain stem to
control the muscles and glands of the body.
 
The brain has three main divisions: (1) the forebrain,(2)
the midbrain, and (3) the hindbrain. Each division has many
parts with special functions. The forebrain includes the
cerebrum which lies toward the top and front of the skull.
The hindbrain lies toward the back and base of the skull.
It includes the medulla oblongata and cerebellum. The
midbrain is the part of the brain stem between the
diencephalon and the medulla oblongata. The brain contains
ventricles (cavities) filled with fluid.
 
The cerebrum is the largest and most important part of the
human brain. It makes up about 85 per cent of the brain
weight. It looks somewhat like hall a shelled walnut. It
consists of two halves, its right and left hemispheres.
Each half is a mirror image of the other and they are
connected by a large bundle of fibers called the corpus
callosum. 

The Diencephalon of the forebrain has three main parts: (1)
the hypothalamus, (2) the subthalamus, and (3) the
thalamus. The hypothalamus, controls such important body
functions as temperature, hunger, and thirst. The
subthalamus contains many fibers and plays an important
part in coordinating movements. The Thalamus is mainly a
distributing center that relays sensory impulses to the
surface of the cerebrum, and from one part of the brain to
another. 

The Midbrain joins the diencephalon and the medulla
oblongata. It has centers that control movements of the
eyes and of other part of the body. 

The Medulla Oblongata is an oblong extension of the spinal
cord into the back of the head. It begins at the base of
the skill, continues upward, and forms the lower part of
the brain stem. The medulla contains nerve centers that
control swallowing, breathing, heartbeat, blood flow,
muscle tone and posture, and movement of the stomach and
intestines. It has centers connected with the organs of
balance in the ears. 

The brain continually gives off small waves of electricity.
To detect these waves, doctors attach wires to the scalp.
Electrically driven pens record the waves on continually
moving strips of paper. This record is called an
electroencephalogram, EEG and helps doctors diagnose
certain brain disorders, including epilepsy and brain
injury. Brain waves become abnormal when the brain is
damaged or the function disturbed. 

Records of the electrical activity of the brain help
scientists discover how the brain works. Using very fine
pointed wires called mocrelectrodes, scientists can study
the activity of a single brain cell.

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