Review of Medical Physiology - William F. Ganong 2002

Functions of the Nervous System
Central Regulation of Visceral Functions
Hypothalamus - Relation to the Regulation of Visceral Functions

Years ago, Sherrington referred to the Hypothalamus as the master ganglion of the Autonomic Nervous system. While stimulation of hypothalamic regions does indeed elicit specific visceral responses, a wealth of evidence suggests that the hypothalamus is not a center for The regulation of visceral Functions per se. Rather, the autonomic responses triggered by the hypothalamus are components of more complex phenomena, such as rage or other emotions.

Effects of Hypothalamic Stimulation

Stimulation of the anterodorsal region of the hypothalamus occasionally induces contraction of the Urinary Bladder musculature, representing a parasympathetic response. However, hypothalamic stimulation elicits very few such responses, making it unlikely that localized parasympathetic centers reside within it.

Stimulation of certain hypothalamic areas can trigger Cardiac Arrhythmias, suggesting that this effect is mediated by the activation of the vagus or sympathetic NERVES OF THE Heart.

Stimulation of various hypothalamic regions, particularly the lateral areas, produces a diffuse sympathetic discharge and increased secretion from The adrenal medulla, akin to the massive sympathetic activation that elicits the "fight-or-flight" stress response in animals (see Chapter 13).

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Fig. 14-3. Secretion of Hypothalamic Hormones. Posterior lobe hormones (34) enter the general Circulation from the axon terminals of the supraoptic and paraventricular nuclei, whereas hypophysiotropic hormones enter the hypophysial portal system from the axon terminals of the arcuate and other hypothalamic nuclei; AL - anterior lobe; MB - mammillary bodies; OC - optic chiasm.

It is hypothesized that distinct areas within the hypothalamus regulate the secretion of epinephrine and norepinephrine. Differential secretion of either catecholamine from the adrenal medulla does occur in certain situations (see Chapter 20), yet the selective increase in secretion in such cases is minor.