Phases of Sleep

By Yolanda Smith, B.Pharm.Reviewed by Benedette Cuffari, M.Sc.

All through wakefulness and sleep, {the electrical} exercise of the mind adjustments and creates various kinds of mind waves. These mind waves are subsequently used to characterize the varied phases of sleep.

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There are two broad phases of sleep which embody fast eye motion (REM) and non-rapid eye motion (NREM). REM and NREM are additional damaged up into three phases, every of which is described in additional element beneath.

Stage 1 NREM sleep

Stage 1 NREM sleep is the preliminary stage of sleep throughout which the person drifts out and in of sunshine sleep and might simply be woke up. The mind exercise throughout this sleep stage is related to alpha and theta waves, decreased exercise of the voluntary muscle groups, and gradual eye motion.

Throughout this stage, it’s common to expertise unusual sensations generally known as hypnogogic hallucinations, similar to a sense of falling and sudden muscle contractions. This stage usually lasts between 5-10 minutes earlier than the person progresses to the subsequent phases of sleep.

Stage 2 NREM sleep

The slowing of mind waves with intermittent bursts of fast mind waves, generally known as sleep spindles, characterizes stage 2 NREM sleep. Moreover, the eyes cease shifting, the physique temperature drops, and the guts price begins to decelerate throughout this stage of sleep. Usually, stage 2 NREM sleep will final for about 20 minutes earlier than the person progresses to the subsequent stage of sleep.

Stage 3 NREM sleep

Stage 3 NREM sleep, which is also called deep sleep or delta sleep, is marked by very gradual delta brainwaves. There isn’t a eye motion or voluntary muscle motion throughout this stage. Moreover, it’s usually tough to wake a person who’s in stage 3 NREM sleep. This stage often lasts for about half-hour earlier than the person progresses to the subsequent phases of sleep.

Beforehand, this stage was cut up into two phases together with stage 3 and stage 4. Stage 3 is built-in with extra fast brainwaves, whereas stage 4 has fixed gradual delta wave mind exercise.

REM sleep

Fast motion of the eyes, short-term paralysis of the voluntary muscle groups, and quick, irregular respiration characterize REM sleep. Throughout this stage, mind waves grow to be quicker and resemble the exercise of an individual who’s awake.

Different adjustments that happen throughout REM sleep embody a rise in coronary heart price and blood strain, in addition to a decreased skill to manage physique temperature. Males may additionally expertise an erection throughout this stage of sleep. Most desires happen throughout REM sleep, though the person will solely bear in mind the desires if they’re awoken on this stage.

Biking via sleep phases

All through the night time, sleep begins with stage 1 NREM sleep and progresses via phases 2 and three to succeed in REM sleep roughly 90 minutes after falling asleep. As soon as the REM sleep stage concludes, mind exercise returns again to stage 2 sleep after which stage 3 sleep, earlier than returning to REM sleep. This cycle often repeats about 4 to 5 instances every night time.

The proportion of various sleep phases will depend on the person. Infants, for instance, will spend roughly 50% of the time that they’re asleep in REM sleep. Comparatively, adults will spend about half of their sleep time in stage 2, 20% in REM, and 30% in phases 1 or 3. As people age, much less time is spent in REM sleep and extra time is as an alternative spent within the different sleep phases.

References

• http://staging.aesnet.org/files/dmfile/Saper1.pdf
• http://www.sleepdex.org/stages.htm
• http://psychcentral.com/lib/stages-of-sleep/
• https://sleepfoundation.org/how-sleep-works/what-happens-when-you-sleep
• http://www.ncbi.nlm.nih.gov/books/NBK10996/

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