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"AND""OR"

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. Copyright © 1996- Studyworld

 



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