A patient asks the nurse to explain how sleep occurs. The nurse explains to the patient that the ...

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The major sleep center in the body is the hypothalamus. The suprachiasmatic nucleus (SCN) nerve cells in the hypothalamus control the rhythm of the sleep-wake cycle and coordinate this cycle with other circadian rhythms. Researchers believe that the ascending reticular activating system located in the upper brainstem contains special cells that maintain alertness and wakefulness. Circadian rhythms influence the 24-hour pattern of major biological and behavioral functions such as the predictable changing of body temperature, heart rate, blood pressure, hormone secretion, sensory acuity, and mood. Sleep causes the basal metabolic rate to fall; falling of the metabolic rate does not cause sleep. Normal sleep involves two phases: nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep.