The Stages of Sleep: The Sleep Cycle Explained

Scientists have identified four main stages of sleep that we go through during the night. Each stage has a significant purpose that makes them important. These are:

  • Stage One: Drowsy Light Sleep
  • Stage Two: Light Sleep
  • Stage Three: Deep Sleep
  • Stage Four: REM (Rapid Eye Movement). This is when dreaming occurs.

These stages typically progress from stage one through to stage four in order, with each stage lasting between 5 to 15 minutes. As the night continues, the REM stage can become longer, even up to an hour towards the end of the night. The complete cycle takes an average of 90 to 110 minutes, and then begins again at stage one.

We also have brief moments of wakefulness during the night, of which we are generally unaware, and these usually it occur at the end of stage four before the cycle restarts at stage one again.

The Stages of Sleep

Stage One

Stage one of sleep is a drowsy light sleep. During this stage, the brain produces alpha and theta waves. There may be slow eye movements, and you can be easily aroused and woken. Muscle tone relaxes, and at this stage some people experience ‘hypnic jerks’, which are sudden involuntary harmless muscle spasms. These jerking movements can be severe enough to wake you up. Taking a brief ‘catnap’ would be classed as resting in stage one of sleep.

Stage Two

Stage two is a light sleep, where slow eye movements may still occur, but you are not aroused or woken quite so easily. The brain produces short sudden bursts of faster brain waves called sleep spindles. Your body temperature will decrease slightly and your heart rate will slow. If you were to ‘power nap’ you would want to wake up after this stage of sleep.

Stage Three

Stage three is a deep sleep. The brain produces slower waves called delta waves. It can be difficult to wake someone from a deep sleep. Sleep talking, sleep walking and night terrors are most likely to happen during this stage. During this sleep period, the body secretes growth hormone. The body repairs and regenerates tissues, bone and muscle, and strengthens the immune system. The heart is slow and regular and the muscles are very relaxed. You rarely dream during this stage and there is no eye movement.

Stage Four

Stage four is when REM (rapid eye movement) sleep occurs. The eyes will move around quickly. You can be woken more easily from this stage, but may feel groggy as a result. This stage is when dreaming occurs as the brain is more active, but the muscles are effectively paralysed so the body is inactive. Heart rate and blood pressure increase and breathing can become faster, irregular and shallow. During REM sleep, emotion, learning and memory are regulated as the brain is consolidating and processing information from the previous day and clearing away things that are not needed.

Excerpt taken from The Science, Techniques and Tips For How to Get to Sleep.

More from Debbie Brewer

Published by debbiebrewerblog

Marking the world with ink and electronic footprints.

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