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Schematic illustration of a normal sleep cycle. The standard figure given for the average length of the sleep cycle in an adult man is 90 minutes. N1 (NREM stage 1) is when the person is drowsy or awake to falling asleep. Brain waves and muscle activity start to decrease at this stage. N2 is when the person experiences a light sleep.
Polyphasic sleep is the practice of sleeping during multiple periods over the course of 24 hours, in contrast to monophasic sleep, which is one period of sleep within 24 hours. Biphasic (or diphasic , bifurcated , or bimodal ) sleep refers to two periods, while polyphasic usually means more than two. [ 1 ]
Known as slow-wave sleep or stage 3 non-REM sleep, this is the deepest stage of sleep and the hardest to wake up from. Brain activity slows down, muscles and bones strengthen, hormones regulate ...
The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in a good night's sleep. [17] [22] The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep. [23]
In a study with 3000 patients, it was found that men and women who sleep less than 5 hours have elevated body mass index (BMI). In another study that followed about 70.000 women for 16 years, there was a significant increase in body weight in those who slept 5 hours or less compared to those who slept 7–8 hours. [1] [2] [8]
Within a few months of postnatal development, there is a marked reduction in percentage of hours spent in REM sleep. By the time the child becomes an adult, he spends about 6–7 hours in NREM sleep and only about an hour in REM sleep. [46] [47] This is true not only of humans, but of many animals dependent on their parents for food. [48]
Cycles of REM and non-REM stages make up sleep. A normal healthy adult requires 7–9 hours of sleep per night. The number of hours of sleep is variable, however the proportion of sleep spent in a particular stage remains mostly consistent; healthy adults normally spend 20–25% of their sleep in REM sleep. [5]
[6] [4] Light seems to have therapeutic antidepressant effects when an organism is exposed to it at appropriate times during the circadian rhythm, regulating the sleep-wake cycle. [ 6 ] [ 4 ] In addition to mood, learning and memory become impaired when the circadian system shifts due to light stimuli, [ 6 ] [ 20 ] which can be seen in studies ...