Once you close your eyes and fall asleep, do you really know what is happening inside your body. Even though you might believe that you are resting, not every part of your body does the same. For example, your brain is sending out a variety of signals, several of which are controlling the different stages of sleep you will be passing through.
The majority of folks assume that their brain is at rest while they are sleeping, but that is most certainly not the case. The truth is that the body rests while asleep, but the brain is very much active. While sleeping, the brain is recharging itself but is also still very much in control of nearly all bodily processes, which includes breathing. Eye movements along with muscle activity also change during the various sleep stages.
Different Stages of Sleep for Humans
Five stages of sleep have been identified and in the course of a good night’s sleep, you will pass through each of them, several times.
While there are five distinct stages, the first four are grouped together and considered the state of NREM or Non-Rapid Eye Movement sleep. The fifth phase is known as the REM or Rapid Eye Movement stage.
The various states of NREM and REM are distinguished by the changes in brainwave activity which take place. REM sleep is also characterized by irregular but rapid breathing and heartbeat, an increase in blood pressure levels, greater brain activity and almost no muscle activity.
NREM and REM sleep occur during the entire sleep period. The sleep which takes place through the first third of a night comprises mainly of NREM while the sleep during the final third is mostly REM. Generally you will wake up from a REM stage.
How Long do Stages of Sleep Last
Phase one is a transitional period that consists of light sleep from which you can easily be awakened. During stage one, the cycle of dropping off to sleep and waking up can repeat itself several times. During this period, you will feel drowsy and begin to lose control over your muscles. Your eye movements will also slow. Additionally, it is during stage one that hypnic myoclonia or an abrupt contraction or jerking of the muscles can take place.
Phase two occupies almost one half of the sleep period. During this time your eyes will stop moving, brain waves will slow, body temperature falls and heart beat slows down. There might be brief bursts of eye movement throughout this stage.
Stages three and four are when your body is in a deep sleep. Both of these sleep stages are characterized by the presence of delta waves, which are brain waves that are exceptionally slow. There is no eye or muscle movement during these two phases.
The REM or Rapid Eye Movement stage occurs during the entire sleep period and always follows a period of NREM sleep. This stage makes up about a quarter of the overall sleep period. The first REM takes place at the end of Stage one and lasts around ten minutes. The final REM stage lasts approximately one hour. If you sleep eight to nine hours, you are likely to experience REM sleep four or five times throughout that period. It is during REM that you are also able to dream.
These stages of sleep repeat through the entire sleep period and are referred to as sleep cycles. Several sleep cycles occur within a single sleep period. As the sleep cycles progress through a sleep period, the quantity of REM sleep increases. Preventing these sleep cycles from being disrupted is what contributes to better sleep quality.