Sleep represents a set of states that are regulated by the brain and have implications for many areas of the body. Sleep is regulated by homeostatic processes that promote both sleep and wake states, as well as circadian processes that regulate the timing of physiologic and behavioral systems. Many of these systems interact with each other, as well as with tissues throughout the body, including immune, cardiovascular, metabolic, musculoskeletal, and sympathetic/parasympathetic systems.
