All About Sleep Cycles and the Stages of Sleep


Like nutrition, we prefer a balanced variety of sleep phases since each serves a purpose. Sleeping well keeps your body, mind, and emotions healthy. Sleeping restores the body, consolidates memories, and induces dreams. Each of the brain's four sleep phases has its own activity pattern and helps ensure a comfortable night.

So, sleep quality matters more than duration. How smoothly we transition between sleep phases affects sleep quality (and spending enough time in the deepest ones). In this article, we'll examine the several sleep stages that make up a regular night's slumber and explore how they help us stay healthy and feel rested when we wake up.

Understanding the Sleep Cycle

Overnight, your brain progresses through a series of sleep stages. For seven to eight hours of sleep, as recommended by Cline, you should go through four to six sleep cycles. The first time around, you'll sleep through each procedure backward. After awakening, you cannot go back to Stage 1. If you're lucky, REM sleep (stages 2 and 3) will follow FREM sleep.

Usually, stage 2 sleep comes after REM sleep. It's possible to briefly wake up during Stage 1 of the sleep cycle and then drift back to sleep. Circadian rhythms that typically last 90 minutes may extend to 120. In fact, the rhythms of sleep shift as the night progress. REM sleep is more common throughout the night and early morning, while stage 3 deep sleep predominates during the first two cycles. Remember that REM and deep sleep help consolidate memories and learn new material.

Sleep Stages

Sleep only follows the four phases perfectly.

After an entire night of unbroken sleep, several steps occur −

  • NREM stage 1 sleep starts.

  • NREM stage 1 becomes stage 2.

  • Next comes NREM stage 3.

  • Eventually, REM slumbers.

After REM sleep, the body returns to NREM stage 2 to restart the cycle.

The cycle repeats throughout the night, varying stage time (about four to five times total).

Sleep architecture describes a person's nighttime cycles. A sleep expert may show you this information on a hypnogram—an EEG graph.

Stage 1 Sleep, or the non-REM Sleep, the First Phase of a Typical Night of Sleep

At this point, we begin to feel ourselves drifting off to sleep. It's possible that the person will not recognize that they were sleeping upon awakening. Starting with a gradual decline from fully awake to a light slumber, Stage 1 of the sleep cycle is the first phase of any given sleep cycle. At this point, you're already well on your way to becoming a deep sleeper. Your breathing, pulse rate, and eye movements all moderate; your muscles loosen up, and your brain's activity decreases.

It's simple to rouse someone in stage 1, but they'll go rapidly to stage 2 if you don't disturb them. Stage 1 sleep often lasts up to ten minutes throughout a normal sleep cycle, especially in the early night hours.

The Second Stage of non-REM Sleep

Heart rate and breathing slow even more when you enter a more profound stage 2 non-REM sleep. The purpose of this stage is to set the scene for the subsequent stages of deep sleep and REM sleep. During deep sleep, a person's core temperature decreases, their muscles relax entirely, and their brain waves decelerate to tiny bursts of electrical activity. Electroencephalograms, which record brain activity while a patient sleep, show that brain wave activity during this period is fascinating. When sleep spindles (brain wave patterns) activate, it means non-rapid eye movement (NREM) sleep is taking place.

Sleep spindle activity suggests that the brain is processing the day's memories while the sensory nerve system (hearing, sight, smell, touch, and taste) shuts down for the night. "It has a great aesthetic value. These neurons act like thread in a sewing machine, moving data from short-term to long-term memory. Researchers believe this message system is how the brain converts newly formed memories into stable long-term memories. Around half the night, or 20 to 60 minutes of every sleep cycle, is spent in stage 2 sleep.

During the third stage of non-REM sleep

You've reached the deepest level of sleep, where you can't even remember what day it is. Now is the time to focus on getting enough sleep, healing your body, and strengthening your immune system. Also, the following day is a far better time for memory encoding after a restful deep sleep. This last phase of non-REM sleep is considered deep sleep, which is necessary to wake up feeling revitalized. Stage 3 is the deepest stage of sleep, during which it is most difficult to be roused since your heart rate and respiration have slowed to their lowest points, and your muscles have been entirely at ease.

 Delta waves, also known as slow-wave sleep, are characteristic of this sleep phase. If you are woken during this period of deep sleep, you may feel groggier than if you were awakened during lighter sleep phases. Research shows that this stage of sleep is when the brain consolidates memories of broad information, such as facts and statistics, while memory consolidation occurs at all phases of sleep. The consolidation of long-term memories, including facts, experiences, geography, and spatial awareness, requires slow-wave sleep. During a typical sleep cycle, we enter a deep sleep stage 3 for 20–40 minutes.

R.E.M., or the Fourth Phase, Refers to the Sleep

REM sleep consolidates memories. REM sleep is characterized by REM. REM is the fourth stage of sleep when brain activity appears awake on brain scans. Blood pressure, pulse, and respiration normalize. Your eyes dart as your muscles freeze. While during REM sleep, it processes more abstract ideas and emotions. The brain reassesses the day's events. Researchers think that REM sleep produces the most lifelike, narrative dreams.

We remember our dreams from the night before since we wake up during this stage of sleep. The brain stores and discards the day's new motor skills during REM sleep. Research reveals that during REM sleep, our brains process further information, solidify memories, and process emotional and traumatic events from the day before. From midnight until daybreak, REM sleep may last one hour (more on that below). Adults spend 25% of their sleep in REM.

Updated on: 10-Mar-2023

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