Sleep and Biological Rhythms

Abstract

The circadian system is responsible for organizing the 24-hour oscillations of many physiological and behavioral processes, including neuroendocrine function, core body temperature, metabolic function, cognitive function, activity, and sleep. Although the circadian system orchestrates the timing of most mammalian physiology and behavior, both the quality and duration of sleep also have significant modulatory effects on many of these physiological and behavioral variables. As a result of the complex and reciprocal interactions of the circadian timekeeping system and sleep, it is impossible for the circadian system to effectively organize physiology and behavior if sleep occurs at a less than optimal time, nor can it perform its job if sleep is of insufficient duration; alterations in the sleep and circadian timing systems have significant consequences for mental and physical well-being, safety, and productivity. In the first part of this chapter we review the anatomical and functional substrates responsible for the generation of sleep and circadian rhythms. Next we highlight the behavioral and physiological processes that are modulated by the reciprocal interaction between circadian rhythmicity and the sleep-wake cycle under normal conditions. The last section is dedicated to pathological conditions that result from disruptions in circadian rhythms, sleep regulation, or both.