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Our Sleep Main Article provides a comprehensive look at the who, what, when and how of Sleep |
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Definition of Sleep
Sleep: The body's rest cycle.
Sleep is triggered
by a complex group of hormones that are active in the main,
and that respond to cues from the body itself and the
environment. About 80 percent of sleep is dreamless, and is
known as non-rapid eye movement (NREM) sleep.
During NREM
sleep, the breathing and heart rate are slow and regular,
the blood pressure is low, and the sleeper is relatively
still. NREM sleep is divided into four stages of increasing
depth of sleep: Level 1 sleep is a transition period
between sleep and wakefulness; Level 2 sleep features
significant slowing of heartbeat and breathing, and makes
up about 50 percent of all sleep; and Level 3 and 4 (Delta)
sleep are marked by very slow respiration and heartbeat.
Level 4 sleep leads to rapid eye movement (REM) sleep, also
known as Level 5 sleep.
Dreams occur during three to five
periods of REM sleep each night. REM sleep occurs at
intervals of one to two hours, and is variable in length.
REM sleep is characterized by irregular breathing and heart
rate, and involuntary muscle jerks.
Most adults need around eight hours of sleep on a regular schedule to function
well, although some require less, and others more. (It has been said that men need an hour less sleep than women.) Children, particularly teenagers, often need nine or ten
hours for optimal functioning.
Last Editorial Review: 11/24/2000
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