hypothalamus

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hypothalamus

(hī'pəthăl`əməs), an important supervisory center in the brainbrain,
the supervisory center of the nervous system in all vertebrates. It also serves as the site of emotions, memory, self-awareness, and thought. Anatomy and Function
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, rich in ganglia, nerve fibers, and synaptic connections. It is composed of several sections called nuclei, each of which controls a specific function. The hypothalamus regulates body temperature, blood pressure, heartbeat, metabolism of fats and carbohydrates, and sugar levels in the blood. Through direct attachment to the pituitary glandpituitary gland,
small oval endocrine gland that lies at the base of the brain. It is sometimes called the master gland of the body because all the other endocrine glands depend on its secretions for stimulation (see endocrine system).
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, the hypothalamus also meters secretions controlling water balance and milk production in the female. The role of the hypothalamus in awareness of pleasure and pain has been well established in the laboratory. It is thought to be involved in the expression of emotions, such as fear and rage, and in sexual behaviors. Despite its numerous vital functions, the hypothalamus in humans accounts for only 1-300 of total brain weight, and is about the size of an almond. Structurally, it is joined to the thalamusthalamus
, mass of nerve cells centrally located in the brain just below the cerebrum and resembling a large egg in size and shape. The thalamus is a routing station for all incoming sensory impulses except those of smell, transmitting them to higher (cerebral) nerve centers.
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; the two work together to monitor the sleep-wake cycle.

Hypothalamus

 

a part of the brain under the thalamus opticus.

The hypothalamus is part of the diencephalon, forming the walls and floor of the third ventricle; the pituitary body, or hypophysis, is suspended from it on a thin stalk. The hypothalamus is an aggregate of higher adaptive centers that integrate and adjust functions to the body’s coordinated activity, playing a major role in maintaining the metabolic level and in regulating the activity of the digestive, cardiovascular, endocrine, and other physiological systems. Thus, the hypothalamus is one of the most important members of a functional system that coordinates autonomic with psychic and somatic functions. It contains more than 30 paired clusters of nerve cells, called nuclei, and it is connected by a large number of neural pathways to the upper and lower divisions of the central nervous system. Certain hormones (for example, vasopressin) and a variety of biologically active substances are formed in the nerve cells of the hypothalamic nuclei. These active substances (the so-called releasing factors) enter the hypophysis by way of the blood vessels and nerve fibers and promote the secretion of hormones.

The hypothalamus exerts neurohumoral and hormonal control over the functions and regulates the activity of the endocrine glands according to the needs of the cells, organs, physiological systems, and the body as a whole. The hypothalamus is furnished with a rich network of blood vessels and receptors that sense the slightest changes in temperature and sugar, salt, water, and hormone content in the internal environment. Fluctuations in the composition and properties of the internal environment trigger corresponding mechanisms that organize feeding and sexual behavior and create the conditions necessary for the maintenance of constant body temperature. Structures that form part of a complex system regulating the alternation and maintenance of sleep and wakefulness are also present in the hypothalamus. The posterior portions of the hypothalamus consist largely of structures that, mostly with the help of the peripheral sym-patheticoadrenal apparatus, provide autonomic and endocrine support for physical and mental activity and adaptation of the body to changes in the external and internal environments (the so-called ergotropic state). The anterior portions of the hypothalamus regulate chiefly the restorative and assimilative processes (the so-called trophotropic state) and maintain the relative constancy of the body’s internal environment (homeostasis). Injury to the hypothalamus results in endocrine, metabolic, trophic, or autonomic disorders, including changes in thermoregulation, sleep and wakefulness, and emotion.

REFERENCES

Fiziologiia i patologiia dientsefal’noi oblasti golovnogo mozga. Moscow, 1963. (Collection of articles.)
Grashchenkov, N. I. Gipotalamus: ego rol’ v fiziologii i patologii. Moscow, 1964.
Fiziologiia i patofiziologiia gipotalamusa. Moscow, 1966.
Monnier, M. Functions of the Nervous System, vol. 1. Amsterdam, 1968.

A. M. VEIN

hypothalamus

[¦hī·pō′thal·ə·məs]
(neuroscience)
The floor of the third brain ventricle; site of production of several substances that act on the adenohypophysis.
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