ABSTRACT
A. Circadian Rhythms, Sleep, and the Autonomic Nervous System The autonomic nervous system is integral to the homeostatic regulatory functions of the sleeping/waking brain. The autonomic changes that occur over the course of the 24-hour of sleep/wake cycle in humans have rhythmic physiological characteristics. Not only do cholinergic, adrenergic, histaminergic, orexin and adenosine neurotransmitters, operating via the brain stem, facilitate the transition between wake and sleep, but they also influence the cycling between non-rapid eye movement (non-REM) and REM sleep. The autonomic system and the sleep/wake system integrate central and peripheral bodily and behavioral functions. A variety of physiological functions under autonomic system control operate within the circadian system in humans. These include the circadian changes in temperature, hormonal, cardiovascular, respiratory, gastrointestinal, and genitourinary functions.
