Respiratory care clinics of North America
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Wakefulness, NREM sleep, and REM sleep are three distinct states of existence. Each state has characteristic behavioral and physiologic patterns,and each has specific neurophysiologic mechanisms associated with its generation and control. Structures in the brainstem use various neurotransmitters to influence higher brain structures in the midbrain and cortex. ⋯ Further progression into the deepest sleep stages 3 and 4 is defined by the occurrence of high-amplitude, low-frequency EEG activity. The progression of sleep stages occurs in cycles of 60 to 120 minutes throughout the sleep period. Various circadian environmental and ontologic factors affect the pattern of sleep stage occurrence.