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The tiny suprachiasmatic nucleus (SCN) of the hypothalamus plays a central role in the daily programming of organismic functions by regulating day-to-day oscillations of the internal milieu and synchronizing them to the changing cycles of day and night and of body state. This biological clock drives the daily expression of vital homeostatic functions as diverse as feeding, drinking, body temperature, and neurohormone secretion. It adaptively organizes these body functions into near-24-hour oscillations termed circadian rhythms. The SCN imposes temporal order 1) through generating output signals that relay time-of-day information, and 2) through gating its own sensitivity to incoming signals that adjust clock timing. |
