What is sleep?
There are over 20 definitions of “sleep” in several dictionaries. The first, a verb, seems most appropriate:
to take the rest afforded by a suspension of voluntary bodily functions and the natural suspension, complete or partial, of consciousness; cease being awake.
Physiologically, sleep is a complex process of restoration and renewal for the body. Scientists still do not have a definitive explanation for why humans have a need for sleep. We do know that sleep is not a passive process or “switching off” of body functions; sleep is believed to be important in many physiologic processes including the processing of experiences and the consolidation of memories. It is also clear that sleep is essential, not only for humans but for almost all animals.
The importance of sleep is underscored by the symptoms experienced by those suffering from sleep problems. People suffering from sleep disorders do not get adequate or restorative sleep, and sleep deprivation is associated with a number of both physical and emotional disturbances. In addition, sleep is influenced by the circadian rhythms (regular body changes in mental and physical characteristics that occur in the course of about 24 hours). These are controlled by brain neurons that respond to light, temperature and hormones and other signals and comprise the body’s biological clock. This clock helps regulate the “normal” awake and sleep cycles. Disruption of these cycles can make people sleepy at times people want to be awake. For example, travelers experience “jet lag” when they cross time zones. When a New Yorker arrives in Paris at midnight Paris time, his or her body continues to operate (their biological clock) on New York time. It may take some time (about 1-3 days) to reset a person’s biologic clock, depending on how much it has been altered by the time change.
There is evidence that some aspects of sleep are under genetic influence; a gene termed DEC2 is being investigated as causing people that possess it to require only about 6 hours of sleep. Researchers have only begun to examine the genetics involved in sleep.
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