Sleep Cycle: The 4 Different Stages Of Sleep

What does REM stand for? REM, also known as paradoxical..

Sleep Cycle: The 4 Different Stages Of Sleep

What does REM stand for?

REM, also known as paradoxical sleep, stands for Rapid Eye Movement. It is a phase of the sleep cycle in which the eyes move rapidly, muscle tone falls and dreams are much more detailed.

We spend the majority of the night sleeping in the non-REM state, which itself can be broken down into four distinct stages.

The stages on non REM sleep are:

NREM Stage 1

This stage occurs after you have decided to sleep and your eyes are closed. During this stage—which typically lasts between 1 and 10 minutes—you are lightly asleep, and you can quickly return to being fully awake.

Defining features

  • Although you are asleep, you may wake up feeling like you didn’t sleep at all.
  • Your body’s muscles are not inhibited yet: your eyes roll a little bit and you may slightly open your eyelids.
  • Breathing slows down and your heartbeat becomes regular.
  • Your blood pressure and brain temperature decrease.
  • The hypnic jerk we sometimes experience when falling asleep, accompanied or not by the sensation of falling down, happens during this stage. Some say it is a vestigial reflex humans developed during the evolutionary process to prevent them from falling off the trees they slept in.

 

Did you know?
People with irregular sleeping habits tend to have these hypnic jerks more often.

NREM Stage 2

When NREM Stage 2 sleep kicks in, things get serious!

Defining features

  • Stage 2 sleep, which usually lasts about 20 minutes, is characterized by a slowing heart rate and a decrease in body temperature. Your body reduces its activity to prepare you to go into a deep sleep.
  • It becomes harder to wake you up.
  • Your brain starts to emit larger waves.
  • Your blood pressure also decreases, and other metabolic functions slow down too.
  • The 2 first stages of NREM Sleep together are often referred to as light sleep.

 

Did you know?

We spend most of our nights in Stage 2 sleep (around 45% of total sleep duration).

NREM Stage 3

This sleep stage refers to the combined stages of what was previously separated into Stage 3 & 4 sleep.

Defining features

  • This stage typically starts 35-45 minutes after falling asleep.
  • As electroencephalograms show, our brain waves slow down and become larger.
  • At this point, you sleep through most potential sleep disturbances (noises and movements) without showing any reaction.
  • If you actually wake up during NREM Stage sleep, there’s a high probability you are going to feel disoriented for the first few minutes.

 

Did you know?

Other names for this stage include “slow-wave sleep” and “Delta sleep.”

REM Stage 4

This is the final stage of a standard sleep cycle. The first Rapid Eye Movement sleep stage lasts around 10 minutes and usually happens after having been asleep at least 90 minutes.

Defining features

  • As its name indicates, your eyes move rapidly in all directions during Rapid Eye Movement sleep.
  • It is during this stage of sleep (the deepest) that powerful dreams usually happen. Same goes for sleepwalking and bedwetting episodes.
  • This stage is also characterized by an increase of the heart and respiration rates, and their rhythms may become irregular.
  • REM stages typically get longer and longer as the night goes by, and the last REM stage can last an hour.

 

*Note: Wrist-worn activity trackers track sleep by analyzing your body movements (actigraphy).

Because the Withings Aura is able to monitor your pulse and respiratory rates as well, it can identify REM sleep in addition to light sleep and deep sleep.

The Sequence of Sleep Stages

Our sleep follows a specific sequence of these different stages. We complete a sleep cycle and begin a new one approximately every 80 to 110 minutes, usually around 90 minutes.

A night’s sleep begins with a light-sleep phase of varying duration, followed by the first deep-sleep phase of the night and a short REM phase.

In the second half of the night, we spend a relatively shorter amount of time in deep-sleep phases while our REM phases tend to be longer.

The final REM phase of the night can last for as long as 30 minutes or more. And then, we wake up.

The pattern of REM sleep changes as we grow older. During the first year of life, babies spend most of their time asleep in REM sleep.

From the age of four, the proportion of REM sleep falls to about 20 percent of the night. People over the age of 60 spend only about 15 percent of the night in REM sleep.

With the exception of infants, people spend most of the night in the light-sleep phase.

If the amount of time we sleep is reduced, it’s the light sleep phase that bears the brunt of the deficit, ensuring we still make it to the deep-sleep phases, which have the most restful effect.

This is why some people can cut their sleeping time right down to a minimum of somewhere between four and six hours, depending on the individual, without losing too much of their capacity the next day.

Nevertheless, we need to spend some time in the light-sleep phase in order to reach the deeper sleep phases. It’s not possible to access deep sleep immediately after falling asleep. Good sleep takes time.

The Purpose of Sleep Stages

Each sleep phase serves a specific purpose for the body.

The primary function of both our light-sleep and deep-sleep phases is to have a regenerative effect on various processes in the body.

During the REM phase, the brain is almost as active as when we are awake. We need both deep sleep and REM sleep to properly process the impressions and memories of the day.

The brain weighs up the information we have taken in while awake and organizes our memories, storing any important information in our long-term memory and discarding superfluous details.

This is why a good night’s sleep is vital for our mental capacity.

If you get an adequate amount of sleep the night before an exam, including several deep-sleep and REM phases, you will be better able to recall the material you have studied.


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Daniel Messer, RNutr, CPT

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