Stage 4

Stage 4

During REM sleep, brain activity picks up, nearing levels seen when you’re awake. At the same time, the body experiences atonia, which is a temporary paralysis of the muscles, with two exceptions: the eyes and the muscles that control breathing. Even though the eyes are closed, they can be seen moving quickly, which is how this stage gets its name.

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Stages of Sleep - Sleep Foundation

sleepfoundation.org

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Different sleep stages.

The classification of sleep stages was update in 2007 by the American Academy of Sleep Medicine (AASM). Before that, most experts referred to five sleep stages, but today, the AASM definitions of the four stages represent the consensus understanding of the sleep cycle.

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Sleep quality > quantity

When thinking about getting the sleep you need, it’s normal to focus on how many hours of sleep you get. While sleep duration is undoubtedly important, it’s not the only part of the equation.

It’s also critical to think about sleep quality and whether the time spent sleeping is actually restorative. Progressing smoothly multiple times through the sleep cycle, composed of four separate sleep stages, is a vital part of getting truly high-quality rest.

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Sleep is not uniform. Instead, over the course of the night, your total sleep is made up of several rounds of the sleep cycle, which is composed of four individual stages. In a typical night, a person goes through four to six sleep cycyles. Not all sleep cycles are the same length, but on average they last about 90 minutes each.

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During stage 2, the body enters a more subdued state including a drop in temperature, relaxed muscles, and slowed breathing and heart rate. At the same time, brain waves show a new pattern and eye movement stops. On the whole, brain activity slows, but there are short bursts of activity that actually help resist being woken up by external stimuli.

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Stage 1 is essentially the “dozing off” stage, and it normally lasts just one to five minutes.

During N1 sleep, the body hasn’t fully relaxed, though the body and brain activities start to slow with periods of brief movements (twitches). There are light changes in brain activity associated with falling asleep in this stage.

It’s easy to wake someone up during this sleep stage, but if a person isn’t disturbed, they can move quickly into stage 2. 

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There are four sleep stages; one for rapid eye movement (REM) sleep and three that form non-REM (NREM) sleep. These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.

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Stage 3 sleep is also known as deep sleep, and it is harder to wake someone up if they are in this phase. Muscle tone, pulse, and breathing rate decrease in N3 sleep as the body relaxes even further.

The brain activity during this period has an identifiable pattern of what are known as delta waves. For this reason, stage 3 may also be called delta sleep or short-wave sleep (SWS).

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Why We Sleep

While even experts haven’t reached a consensus explanation for why we sleep, numerous indicators support the view that it serves an essential biological function.

In adults, a lack of sleep has been associated with a wide range of negative health consequences including cardiovascular problems, a weakened immune system, higher risk of obesity and type II diabetes, impaired thinking and memory, and mental health problems like depression and anxiety.

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How Sleep Works: Understanding the Science of Sleep | Sleep Foundation

sleepfoundation.org

Snoring isn’t harmful

Although snoring may be harmless for most people, it can be a symptom of a life-threatening sleep disorder called sleep apnea, especially if it is accompanied by severe daytime sleepiness. 

Sleep apnea can be treated; men and women who snore loudly, especially if pauses in the snoring are noted, should consult a physician.

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Myths and Facts about Sleep - National Sleep Foundation

sleepfoundation.org

The average adult spends 36 % (or about one-third) of his or her life asleep.

Purpose of Sleep:

  • Restoration
  • Memory Consolidation
  • Metabolic Health

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The Science of Sleep: A Brief Guide on How to Sleep Better Every Night

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