In order to get a proper night’s sleep, the body must pass through various stages of sleep.  For most people, failure to go through each of these stages will result in a feeling of having poor quality sleep.  As a result, the person may have cognitive problems and memory problems.  He or she may also experience a general feeling of moodiness or crankiness.

 

Rapid Eye Movement

 

The first broad stage of sleep is called Rapid Eye Movement, or REM.  During this stage, the brain is quite active while the body remains inactive.  Since the brain is so active during the REM stage, most dreaming occurs during this stage. 

 

When measuring brain activity, the brain actually experience a low voltage of mixed frequency activity that is similar to when awake.  In addition, the sympathetic nervous system is active at this time.  At the same time, the body experiences a reduction in skeletal muscle tone during the REM stage.

 

Non-Rapid Eye Movement

 

The other broad stage of sleep is referred to as Non-Rapid Eye Movement (NREM).  During NREM sleep, the body becomes inactive while the body is active.  As such, there is generally very little dreaming during the NREM stage.  On the other hand, limb movement or sleep walking may take place during this stage of sleep. 

 

While in the NREM stage, the body passes through four substages.  The first two stages are considered light sleep while the second two stages are considered deep sleep.  The ability to recognize these various stages is only accomplished through EEG readings. 

 

Approximately 75-80% of the time spent sleeping is in the NREM stage.  During the first stage, which is often referred to as “drowsy sleep,” the person may experience jerking and twitching.  Some also experience hallucinations, which can be problematic for the person.  The person also experiences a loss of muscle tone but is still aware of his or her surroundings.

 

During stage 2, the person is no longer aware of his or her surroundings.  This stage accounts for 45-55% of the total time spent sleeping.  During stage 3, a person may begin experiencing night terrors, sleepwalking, bed wetting, and sleep talking.  Stage 4, on the other hand, is a deeper version of stage 3.

 

After completing these four stages of NREM sleep, the body transitions into REM sleep.  This is when dreaming most commonly occurs and typically happens during the last third of the entire sleeping period. 

 

Sleep in Newborns

 

Research has found that newborn babies experience an additional stage of sleep that is similar to the REM stage.  This is referred to as active sleep.  In addition, the cycles of newborns are often divided into three stages:  active sleep, quite sleep, and then the wake stage.  These stages are based mostly upon making behavioral observations because it is very difficult to perform an EEG on newborns in order to monitor the activity that takes place in the brain while sleeping.  The slight differences in newborn sleep when compared to adult sleep is largely attributed to the fact that the newborn’s central nervous system is still in development.