subject: The States Of Sleep [print this page] The States Of Sleep The States Of Sleep
There are two states of normal human sleep: nonrapid eye movement sleep, or NREM sleep, and rapid eye movement sleep, or REM sleep. NREM and REM sleep usually alternate in cyclically with each other. under normal circumstances, you enter sleep through NREM sleep and this cycles with REM sleep at about 90110 minute intervals. Young adults usually experience 4 to 5 REM periods throughout the time they are asleep.
NREM sleep comprises light sleep and also slow wave sleep. By convention, NREM sleep is subdivided into 4 stages. Stages 1 and 2 are considered to be light sleep and stages 3 and 4 are called slow wave sleep. The 4 stages of NREM sleep parallel the depth of sleep. You are therefore most likely to waken easily in stage 1 and be very difficult to waken in stage 4 sleep. The best way to think of NREM sleep is as "a relatively inactive yet actively regulating brain in a movable body."
During REM sleep we have significant brain activity along with muscle atonia, which means that our muscles are effectively paralyzed, except for the muscles that move the eyes, the diaphragm (for breathing), and the heart. During REM sleep we experience episodic bursts of rapid eye movements. This is the period when we experience dreams. If woken from this stage of sleep, you are likely to have vivid dream recall about 80 percent of the time. The best way to think of REM sleep is as "a highly activated brain in a paralyzed body."
Sleep occurs in cycles. The first cycle begins with stage 1 NREM sleep, when it is easy to wake someone. Stage 2 nreM sleep has a higher arousal threshold. This stage lasts about 1025 minutes. Stages 3 and 4 of NREM sleep are characterized by slow wave sleep, which takes up about 2040 minutes in the first sleep cycle. Body movement and lightening of sleep occurs within about 510 minutes of stage 2 prior to going into the first episode of REM sleep of the night. This first period of REM sleep usually lasts for 15 minutes.
NREM and REM stages of sleep alternate throughout the night in a circadian rhythm. In adults, the average duration of the first sleep cycle of the night is 70100 minutes and later cycles last about 90120 minutes. Slow wave sleep is dominant in the first third of the night and REM sleep is dominant in the last third. This is why we generally wake up from a dream or just after a dream in the morning.
