Many physiological variables are controlled during wakefulness at levels that are optimal for the body’s functioning. Sleep is a state that is relatively easy to reverse (this distinguishes sleep from other states of reduced consciousness, such as hibernation and coma).įrom observations of behavioral changes that accompany sleep and simultaneous physiological changes, scientists now define sleep in humans based on brain wave activity patterns and other physiological changes as described below.Sleep results in a decreased responsiveness to external stimuli.Sleep is associated with a typical posture, such as lying down with eyes closed in humans.From observing changes in behavior and responsiveness, scientists have noted the following characteristics that accompany and in many ways define sleep: All organisms exhibit daily patterns of rest and activity that resemble the daily sleep and wakefulness patterns seen in humans. Thus, although everyone sleeps, most people would be hard-pressed to precisely define sleep. Except in rare instances, we never contemplate and appreciate that we are sleeping while we are asleep. When we wake, we typically remember little or nothing about the hours that have just passed. During some stages of sleep the brain is just as active as when we are fully awake.Įvery night, nearly every person undergoes a remarkable change: we leave waking consciousness and for hours traverse a landscape of dreams and deep sleep.
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