Five Stages of Sleep - REM Sleep Stages

When you close your eyes and drop off to sleep, do you really know what is going on inside your body. Although you may think that you are at rest, not every part of your body is doing the same. For instance, the brain is sending out all sorts of signals, many of which are controlling the various stages of sleep you will be going through.

Many people believe that their brain is at rest while they are sleeping but that is certainly not the case. It is true that the human body rests during sleep but the brain is very much active. During sleep the brain is recharging its batteries but is still very much in control of the majority of bodily functions, including breathing. Eye movements and muscle activity also change during the various sleep stages.

Five stages of sleep have been identified and during a good night's sleep, you will pass through all of them, several times. Although there are five distinct stages, the first four are grouped together and classified as the state of NREM or non rapid eye movement sleep. The fifth stage is considered the REM or rapid eye movement stage.

The different states of NREM and REM are distinguished by the changes in brain wave activity that takes place. REM sleep is also characterized by irregular but rapid breathing and heartbeat, a rise in blood pressure, increased brain activity and virtually no muscle activity.

NREM and REM sleep take place throughout the sleep period. The sleep that takes place during the first third of a night consists mostly of NREM while the sleep during the last third is mostly REM. Usually you will awaken from a REM stage.

Stage one is a transitional period which consists of light sleep from which you can easily be awakened. During stage one, the cycle of falling asleep and waking can repeat itself several times. During this stage you feel drowsy and begin to lose control over your muscles and your eye movements slow. It is also during stage one that hypnic myoclonia or a sudden contraction or jerking of the muscles can occur.

Stage two occupies nearly half of the sleep period. During this period the eyes will stop moving, brain waves slow, body temperature drops and heart beat slows. There may be short bursts of eye movement during this stage.

Stages three and four are the when the body is in a deep sleep. These two sleep stages are characterized by the presence of delta waves which are brain waves that are extremely slow. There is no eye or muscle movement during these two stages.

The REM or Rapid Eye Movement stage takes place throughout the sleep period and always follows a period of NREM sleep. This stage accounts for about a quarter of the total sleep period. The first REM occurs at the end of Stage one and lasts about ten minutes. The final REM stage lasts about an hour. If you sleep eight to nine hours, you will typically experience REM sleep four or five times during that time. It is during REM that you are also able to dream.

These sleep stages repeat throughout the sleep period and are known as sleep cycles. Several sleep cycles take place during a single sleep period.

As the sleep cycles progress through a sleep period, the amount of REM sleep increases. Keeping these sleep cycles from becoming disrupted is what results in better quality sleep.