Stages Of Sleep

Stages of Sleep
Usually sleepers go through five stages: 1, 2, 3, 4 and REM (rapid eye movement) sleep. These stages progress cyclically from 1 through REM then begin again with stage 1.
Acomplete sleep cycle takes an average of 90 to 110 minutes. The first sleep cycles each night have relatively short REM sleeps and long periods of deep sleep but later in the night, REM periods lengthen anddeep sleep time decreases.
Stage 1 is light sleep where you drift in and out of sleep and can be awakened easily. In this stage, the eyes move slowly and muscle activity slows. During this stage,many people experience sudden muscle contractions preceded by a sensation of falling.
In stage 2, eye movement stops and brain waves become slower with only an occasional burst of rapid brain waves.When a person enters stage 3, extremely slow brain waves called delta waves are interspersed with smaller, faster waves. In stage 4, the brain produces delta waves almost exclusively. Stages 3 and 4 arereferred to as deep sleep or delta sleep and it is very difficult to wake someone from them. In deep sleep, there is no eye movement or muscle activity. This is when some children experiencebedwetting, sleepwalking or night terrors. In 2008 the sleep profession in the US eliminated the use of stage 4. Stages 3 and 4 are now considered stage 3.
In the REM period, breathing becomes more rapid,irregular and shallow, eyes jerk rapidly and limb muscles are temporarily paralyzed. Brain waves during this stage increase to levels experienced when a person is awake. Also, heart rate increases, bloodpressure rises, and the body loses some of the ability to regulate its temperature. This is the time when most dreams occur, and, if awoken during REM sleep, a person can remember the dreams. Mostpeople experience three to five intervals of REM sleep each night.
Infants spend almost 50% of their time in REM sleep. Adults spend nearly half of sleep time in stage 2, about 20% in REM and the...