Stages of Sleep. Usually sleepers pass through five stages: 1, 2, 3, 4 and REM (rapid eye movement) sleep. These stages progress cyclically from 1 through REM then begin again with stage 1. A complete sleep cycle takes an average of 90 to 110 minutes. The first sleep cycles each night have relatively short REM sleeps and long periods of deep sleep but later in the night, REM periods lengthen and deep sleep time decreases.
http://www.sleepdex.org/stages.htm
In stage 4, the brain produces delta waves almost exclusively. Stages 3 and 4 are referred to as deep sleep or delta sleep, and it is very difficult to wake someone from them. In deep sleep, there is no eye movement or muscle activity.
http://www.sleepdex.org/stages.htm
Historically, what is now usually described as stage 3 (following the guidelines of the American Academy of Sleep Medicine) was split into two stages, stage 3 and stage 4, depending on the frequency of delta waves (stage 4 was initially defined as when delta waves exceeded 50% of the total).
http://www.howsleepworks.com/types_nonrem.html
Stage 2 (NREM2 or N2) is the first unequivocal stage of sleep, during which muscle activity decreases still further and conscious awareness of the outside world begins to fade completely. If any sounds are heard, the sleeper is not able to understand their content at this point.
http://www.howsleepworks.com/types_nonrem.html
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Next comes Stage N3, sometimes referred to as Delta Sleep or slow wave sleep, because of the slow delta brain waves, which have been recorded during this sleep stage. N3 sleep is a regenerative period where your body heals and repairs itself. The first episode of Stage N3 lasts from 45-90 minutes.
http://www.sleepapnea.org/learn/healthy-sleep/importance-of-sleep-understanding-sleep-stages.html
Source: Boundless. “Stages of Sleep.” Boundless Psychology. Boundless, 25 Aug. 2015. Retrieved 11 Oct. 2015 from https://www.boundless.com/psychology/textbooks/boundless-psychology-textbook/states-of-consciousness-6/sleep-and-dreaming-42/stages-of-sleep-182-12717/.
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Sleep, stages of sleep,stage 1 NREM, stage 2 NREM, stage 3 NREM, stage 4 NREM, sleep disorders, insomnia, sleep apnea, narcolepsy, RLS, Alternative therapies, mind-body medicine, integrative therapies .. http://wikiofscience.wikidot.com/science:sleep Wikidot CC BY.
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(NREM = Non REM sleep). During the course of an eight hour sleep period, a healthy sleeper should cycle through the various sleep stages every 90 minutes or so. Stage N1 (NREM1) sleep is a transition period from being awake to falling asleep. During this time you may have a sudden dream onset.
http://www.sleepapnea.org/learn/healthy-sleep/importance-of-sleep-understanding-sleep-stages.html
Stage R is referred to as REM sleep or “rapid eye movement” sleep. The first REM sleep episode generally occurs after 90-110 minutes of sleep, cycling about every 90 minutes thereafter. REM sleep periods tend to be longer later in the night. Our heart and breathing rates increase and become irregular.
http://www.sleepapnea.org/learn/healthy-sleep/importance-of-sleep-understanding-sleep-stages.html
what stage of sleep is referred to as delta sleep
3 and 4 stage of sleep is referred to as delta sleep. The stage 3 and 4 is referred to as delta sleep.