Stages of Sleep

Throughout wakefulness and sleep, the electrical activity of the brain changes and creates different types of brain waves. These brain waves are therefore used to characterize the various stages of sleep.

Image Credit: javi_indy / Shutterstock.com

There are two broad stages of sleep which include rapid eye movement (REM) and non-rapid eye movement (NREM). REM and NREM are further broken up into three stages, each of which is described in more detail below.

Stage 1 NREM sleep

Stage 1 NREM sleep is the initial stage of sleep during which the individual drifts in and out of light sleep and can easily be awakened. The brain activity during this sleep stage is associated with alpha and theta waves, reduced activity of the voluntary muscles, and slow eye movement.

During this stage, it is common to experience strange sensations known as hypnogogic hallucinations, such as a feeling of falling and sudden muscle contractions. This stage typically lasts between 5-10 minutes before the individual progresses to the next stages of sleep.

Stage 2 NREM sleep

The slowing of brain waves with intermittent bursts of rapid brain waves, known as sleep spindles, characterizes stage 2 NREM sleep. Additionally, the eyes stop moving, the body temperature drops, and the heart rate begins to slow down during this stage of sleep. Typically, stage 2 NREM sleep will last for approximately 20 minutes before the individual progresses to the next stage of sleep.

Stage 3 NREM sleep

Stage 3 NREM sleep, which is also known as deep sleep or delta sleep, is marked by very slow delta brainwaves. There is no eye movement or voluntary muscle movement during this stage. Furthermore, it is often difficult to wake an individual who is in stage 3 NREM sleep. This stage usually lasts for approximately 30 minutes before the individual progresses to the next stages of sleep.

Previously, this stage was split into two stages including stage 3 and stage 4. Stage 3 is integrated with more rapid brainwaves, whereas stage 4 has constant slow delta wave brain activity.

REM sleep

Rapid movement of the eyes, temporary paralysis of the voluntary muscles, and fast, irregular breathing characterize REM sleep. During this stage, brain waves become faster and resemble the activity of a person who is awake.

Other changes that occur during REM sleep include an increase in heart rate and blood pressure, as well as a reduced ability to regulate body temperature. Males may also experience an erection during this stage of sleep. Most dreams occur during REM sleep, although the individual will only remember the dreams if they are awoken in this stage.

Sleep (Cycle, EEG Waveforms, Pathology)

Cycling through sleep stages

Throughout the night, sleep begins with stage 1 NREM sleep and progresses through stages 2 and 3 to reach REM sleep approximately 90 minutes after falling asleep. Once the REM sleep stage concludes, brain activity returns back to stage 2 sleep and then stage 3 sleep, before returning to REM sleep. This cycle usually repeats about four to five times each night.

The proportion of different sleep stages depends on the individual. Infants, for example, will spend approximately 50% of the time that they are asleep in REM sleep. Comparatively, adults will spend about half of their sleep time in stage 2, 20% in REM, and 30% in stages 1 or 3. As individuals age, less time is spent in REM sleep and more time is instead spent in the other sleep stages.

References

Further Reading

Last Updated: Apr 8, 2023

Yolanda Smith

Written by

Yolanda Smith

Yolanda graduated with a Bachelor of Pharmacy at the University of South Australia and has experience working in both Australia and Italy. She is passionate about how medicine, diet and lifestyle affect our health and enjoys helping people understand this. In her spare time she loves to explore the world and learn about new cultures and languages.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Smith, Yolanda. (2023, April 08). Stages of Sleep. News-Medical. Retrieved on October 31, 2024 from https://www.news-medical.net/health/Stages-of-Sleep.aspx.

  • MLA

    Smith, Yolanda. "Stages of Sleep". News-Medical. 31 October 2024. <https://www.news-medical.net/health/Stages-of-Sleep.aspx>.

  • Chicago

    Smith, Yolanda. "Stages of Sleep". News-Medical. https://www.news-medical.net/health/Stages-of-Sleep.aspx. (accessed October 31, 2024).

  • Harvard

    Smith, Yolanda. 2023. Stages of Sleep. News-Medical, viewed 31 October 2024, https://www.news-medical.net/health/Stages-of-Sleep.aspx.

Comments

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment
Post

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Poor sleep quality linked to increased brain aging in middle age