Posted by Q (198.64.206.92) on January 29, 2000 at 03:33:03:
In Reply to: Weekend Discussions begins! Topic 1 posted by Elaine on January 28, 2000 at 07:27:50:
The Hypothalamus
The hypothalamus is a region of the brain, roughly the size of a cherry, situated behind the eyes and directly under the thalamus. The hypothalamus has nerve connections to most other regions of the nervous systems.
Function -- It exerts overall control over the sympathetic nervous system.
When we are suddenly alarmed or excited, signals are sent from higher regions of the brain to the hypothalamus, which initiates sympathetic nervous system activity which results in the “fight or flight” response.
Other groups of nerve cells in the hypothalamus are concerned with the control of body temperature. Some are sensitive to heat or cold so that, when blood flowing to the brain is hotter or colder than normal, the hypothalamus switches on the temperature regulating mechanisms (among them are sweating or shivering).
The hypothalamus receives information from the body’s sense organs regarding the level of glucose in the blood and in the body’s water content. If they are too low, it stimulates appetite for food and water.
The hypothalamus is also involved in regulating sleep, in motivating sexual behavior, and in determining mood and the experience of emotions.
Another role of the hypothalamus is coordination of the function of the nervous and endocrine (hormonal) systems of the entire body. The hypothalamus connects to the pituitary gland through a short stalk of nerve fibers and controls the hormonal secretions from this gland. It does this in two ways – through direct nerve connections and through specialized nerve cells, which secrete hormones called releasing factors into the blood and flow directly to the pituitary. In this way, the hypothalamus can convert nerve signals into hormonal signals. Thus, the hypothalamus indirectly controls many of the endocrine organs, including the pituitary, thyroid, adrenal cortex and gonads.
The hypothalamus coordinates the endocrine (hormonal) system and thereby indirectly controls the adrenal cortex and thereby the release of adrenaline.
Disorders – Disorders of the hypothalamus are usually caused by brain hemorrhage within the hypothalamic region (see intercerebral hemorrhage) or by an expanding pituitary tumor.
Loss of hypothalamic function can have diverse effects, ranging from hormonal disorders to disturbed temperature regulation, and increased or decreased appetite for food, sex and sleep.
Source: American Medical Association Encyclopedia of Medicine - Randon House, 1989