Hypothalamus

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Hypothalamus, part of the brain, important in regulating the internal activities of the body. Although the hypothalamus constitutes less than 1 percent of the total volume of the brain, it has an important influence on many of the body's functions, including sexual behavior, emotions, hormone production, and the autonomic nervous system.

ANATOMY

The human hypothalamus weighs about 4 g (0.14 oz) and is found behind the eyes, directly below the brain's thalamus and above the pituitary gland. The hypothalamus is divided into several distinct nuclei, that is, aggregates of nerve cell bodies. These nerves connect the brain with the hypothalamus and the hypothalamus to virtually all regions of the nervous system. The hypothalamus also receives nerve inputs from the erogenous zones (the genitalia and nipples), the viscera (internal organs), and the limbic system (concerned with motivation and drive).

FUNCTION

The hypothalamus controls a wide range of functions. It directs the “fight or flight” response of the autonomic nervous system. Fear or excitement causes signals to travel to the hypothalamus, which triggers a rapid heartbeat, faster breathing, widening of the pupils, and increased blood flow. The hypothalamus monitors blood glucose levels and the body's water content to regulate appetite for food or drink. It regulates sleep and sexual behavior.

ENDOCRINE FUNCTIONS OF THE HYPOTHALAMUS

The hypothalamus is responsible for controlling the hormones released from the pituitary gland. Two of these hormones are oxytocin and vasopressin (also called antidiuretic hormone or ADH).

Oxytocin plays a role in uterine contractions during childbirth. It also has a role in starting and maintaining the birth process. Breastfeeding also triggers the secretion of oxytocin via a nervous pathway that connects the nipple and the hypothalamus; oxytocin stimulates the flow of milk from the breast to the infant. Oxytocin secretion can also be caused by the sound of a baby crying—an example of the connections the hypothalamus has with the other parts of the brain.

See also HYPOTHALAMUS DISORDERS

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