Stages of
Sleep
Usually sleepers pass 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. A complete 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 and
deep sleep time decreases.
Stage 1 is a transition state between sleeping and waking. In this stage, the eyes
move more slowly and muscle activity slows as well. Stage 1 is a light sleep
where you can be awakened easily.
In stage 2, eye movement stops and brain waves become slower with only an occasional burst . At this point, the body prepares to enter deep sleep. 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 are referred 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 experience bedwetting, 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 stage 2, eye movement stops and brain waves become slower with only an occasional burst . At this point, the body prepares to enter deep sleep. 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 are referred 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 experience bedwetting, 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.
Slow wave sleep comes mostly in the first half of the night, REM in the
second half. Waking may occur after REM. If the waking period is
long enough, the person may remember it the next morning. Short
awakenings may disappear with amnesia.
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, blood pressure rises, males
develop erections 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. Most people 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 other 30% is divided
between the other three stages. Older adults spend progressively less time in
REM sleep.
