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Sleeping Basics |
Sleeping Problems (Home) > Sleeping Basics > Stages of Sleep Stages of SleepSleep is a dynamic process during which parts of the brain can be very active. There are five recognized stages of sleep, each of which is characterized by different types of brain activity:
Stages 1 through 4 are also known as Non-Rapid Eye Movement (NREM) Sleep. The body cycles through the different sleep stages from stage 1 to REM, and then begins the cycle again with stage 1, throughout the rest period. Each stage represents a different physical and mental state of the body. During some stages, the body is in a lighter sleep and can be awakened more easily, while others indicate a very deep sleep. All are essential to a proper night's sleep. Stage 1 is a period of drowsiness during which the muscles begin to relax, the eyes move very slowly, and a person can be easily awakened. In Stage 1, we may drift in and out of sleep for about 5 to 10 minutes before moving onto the next stage of sleep.
Stage 2 sleep is a deeper sleep than Stage 1, but it is still classified as light sleep, where eye movement stops and brain activity slows down with occasional bursts of rapid waves, called sleep spindles. Also during Stage 2, the heart rate drops and body temperature decreases. Stages 3 and 4 comprise deep sleep, during which all eye and muscle movement ceases. In these stages, it can be difficult to wake a person. Stage 3 is characterized by very slow brain waves (called delta waves), interspersed with smaller, faster waves. In Stage 4 sleep, the brain waves are virtually all very slow delta waves. Stage 3 and 4 sleep is often called Slow Wave Sleep (SWS) for this reason. It is very difficult to wake someone during Stages 3 and 4, and during these deep stages of sleep some people may experience sleepwalking or night terrors, and children may experience bedwetting. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. It is during REM sleep that dreams occur. Also during REM sleep, the muscles of the body stiffen the limb muscles may become temporarily paralyzed, the eyes move rapidly in various directions, the heart rate increases, breathing becomes more rapid and irregular, and the blood pressure rises. Males may also develop penile erections. Normally, approximately 50% of sleep time is spent in Stage 2 sleep, and about 20% is spent in REM sleep. For an average 8 hours of sleep, about 4 hours are spent in Stage 2 sleep and 1.5 to 2 hours are REM sleep. The remaining 30 percent of sleep time is split among the other stages. After a person falls asleep, the first REM sleep period generally happens 70-90 minutes later. A complete sleep cycle, from the beginning of stage 1 to the end of REM, usually takes about an hour and a half to an hour and 50 minutes. These sleep stages cycle through and occur multiple times during an average night of sleep. On average, a person will cycle through the all of the stages of sleep four or five times in an eight hour rest period. The first cycles of the stages of sleep of the night tend to have shorter REM periods and longer periods of deep sleep (Stages 3 and 4). However, as the rest period progresses, this trend reverses and the later cycles have longer REM periods and shorter deep sleep periods (Stages 3 and 4). Towards the end of the rest period, most sleepers spend almost all of their time in stages 1, 2 and REM sleep with very little deep sleep (Stages 3 and 4). Infants are unique in that they spend approximately 50 percent of their sleep time in REM sleep.REM and deep sleep (Stages 3 and 4) are particularly important stages of a normal sleep cycle.
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Stage of Sleep, Five Stage of Sleep, Stage of the sleep cycle.
