What Happens When You Sleep?

July 26, 2010 by  
Filed under Sleep

The sleep process is a series of brain activity cycles. REM sleep is characterized by Rapid Eye Movement. NREM (Non-rapid eye movement) sleep goes through four stages.

Sleep begins with NREM sleep, with each of the four stages generally lasting from five to fifteen minutes.

In Stage 1, the eyes are closed, and the person awakens easily. One may experience a feeling of falling, or involuntary muscle contractions. Stage 2 is characterized by a slowing heart rate, and temperature of the body decreases. Stage 3and 4 are stages of deep sleep, during which the body repairs itself, builds muscle and bone, and strengthens the immune system. If awakened during this state, the person may be disoriented.

The first REM stage usually begins after about 90 minutes of NREM sleep. The first REM stage is about 10 minutes long; each REM stage is longer, with the final one up to an hour in length. During REM sleep, both respiration and heart rate are fast and erratic, along with eye movement.

An increase in brain activity during REM sleep produces vivid dreams. At the same time, the person experiences paralysis in major muscle groups. There are several theories, one of which is that during REM sleep, one part of the brain is “filing” the day’s observations and memories, and another part of the brain is attempting to link them into a single “story” resulting in some of the odd dreams people experience. Scientists also theorize that the muscle paralysis may occur in order to prevent physical harm from the body “acting out” the dreams.

As the body ages, there are changes in sleep patterns. Babies are in the REM state about 50% of the time, while adults are in REM about 20% of the time. Adults spend less time in deep sleep, and the sleep cycles grow shorter.

There have been numerous tests to determine the effect of disruption of the sleep cycle. Disruption of the sleep cycle affected memory in different ways, depending upon when the interruptions occurred.

Other studies confirmed that adequate sleep promoted optimal wound healing and immune system effectiveness, while sleep deprivation had a negative effect on both.

REM sleep has been shown to be critical in brain development. Sleep deprivation in early life can lead to significant behavioral problems, as well as later developmental disabilities.

The sleep cycle is regulated by the circadian clock—an inner timer that regulates sleep, temperature, and enzymes within the body.


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