Weekly Topic...
Know your
sleep
Normal
sleep progressively passes through five stages. The stages of sleep are defined by their
associated electrical patterns in the brain. While a person sleeps, it is possible to
detect these patterns with a device which senses the electrical activity in the brain,
called an electroencephalogram (EEG).
During the
first four stages of sleep, the muscles of the eyes are relaxing. These stages are
collectively referred to as non-rapid eye movement (NREM) sleep.
The last
stage of sleep is associated with increased contraction of the eye muscles. As a result,
the fifth stage of sleep (when eye movement is active) is called rapid eye movement sleep
or REM sleep.
Sleep
requirements vary from person to person. Some individuals may be refreshed upon awakening
after only four to five hours of sleep, while others need far more than the average (eight
hours). The feeling of inadequate sleep despite an adequate opportunity to sleep is
referred to as insomnia.
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 -
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.
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