The primary function of the autonomic nervous system (ANS) is maintenance of homeostasis controlling involuntary functions of the body such as circulation and heart rate, respiration, thermoregulation, neuroendocrine secretion, and gastrointestinal and genitourinary function. Sleep–wake cycle control and ANS are intimately related on an anatomical, physiological, and neurochemical basis. Ans function state-dependent changes have been well recognized and described. The first to understand the importance of ANS modifications during sleep stages in clinical medicine were Lugaresi and colleagues in the early 1970s who described the dramatic changes in systemic and pulmonary blood pressure (BP) associated with apneas and renewal of breathing in patients with Pickwick's syndrome. Sleep and ANS interactions The major confirmation of the relationship between sleep and ANS is the presence of dynamic synchronous fluctuations in sleep phases and autonomic functions. Sleep state changes are co-ordinated principally by the pons, basal forebrain areas, and other subcortical structures, and the main neurotransmitters are norepinephrine, serotonin, and acetylcholine. The same neuronal population that produces and distributes these neurotransmitters constitutes the central anatomical substrate of the sympathetic and parasympathetic nervous systems. The central autonomic network, through its ascending and descending connections between the hypothalamic-limbic region and the nucleus tractus solitarius in the medulla, orchestrates the two divisions of the ANS. Sleep induces profound changes in ANS functions and disorders of ANS affect vital functioning during sleep including circulation and respiration. Non-rapid eye movement (NREM) sleep is characterized by electrocortical synchronization, reduced muscle tone, and stable parasympathetic predominance.
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