Brain
The brain is part of the central nervous system which is contained within the cavity of the cranium. It is mainly composed of nerve cells. The brain can be divided into three areas: hindbrain, midbrain, and forebrain.
The hindbrain, or brain stem, is composed of three structures: pons, medulla oblongata, and cerebellum. It is located in the posterior, caudal regions of the cranium.
The pons is a band of nerve axons, which act as a communication bridge between the cerebellum and the medulla oblongata. The medulla oblongata is composed of cranial nerves and nerves which control the vital reflexes for breathing, heart rate, and blood pressure.
There are 12 pairs of cranial nerves. Cranial nerves carry information in and out of the brain. Some are involved in very specialized sensory functions such as smell, sight, and sound; others are involved in muscular control. The cerebellum is a bilobed structure which looks like a separate structure, but is attached to, and is part of, the brain stem. It coordinates voluntary muscle movements and skeletal muscles which are involved in maintaining equilibrium. The hindbrain is the signal relay area between the higher centers of the brain and the rest of the body.
The midbrain includes the reticular formation and some cranial nerves. Collectively, it is involved in coordination of movement, contains reflex centers for sight and hearing, and is involved in sleeping, waking, and alertness. It also facilitates or inhibits signals going to and from the higher centers of the brain.
The forebrain is composed of the two lobes of the cerebrum and the diencephalon. The diencephalon includes the two thalami and the hhypothalamus. Each thalamus is involved in the control of muscular activity. The hypothalamus is involved in the control of the pituitary gland. The highly invaginated outermost layer of the cerebrum is termed the cerebral cortex. The cerebral cortex is approximately three millimeters thick and is an area of gray matter. This area is believed to be the highest center of control and integration of the central nervous system, the site where thought, memory, and emotions are theorized to occur.
The entire brain and spinal cord are covered by three membranes and surrounded by cerebrospinal fluid, a clear, colorless fluid which protects the brain.
References
Gray, H. 1977. Gray's Anatomy. Crown Publishers, Inc, New York. 1257 pp.
Van Amerongen, C. The Way Things Work; Book Of The Body. New York: Simon and Schuster, 1979.
Vander, A.J., J.H. Sherman, et. al. 1980. Human Physiology The Mechanisms of The Body Functions. Mcgraw-Hill. New York. 724 pp.
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