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The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep. It is sometimes called the ultradian sleep cycle, sleep–dream cycle, or REM-NREM cycle, to distinguish it from the circadian alternation between sleep and wakefulness. In humans, this cycle takes 70 to 110 minutes (90 ± 20 minutes). [1]
The basic rest–activity cycle (BRAC) is a physiological arousal mechanism in humans proposed by Nathaniel Kleitman, [1] hypothesized to occur during both sleep and wakefulness. Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes [ 2 ] ) characterized by different levels of excitement and rest.
NREM sleep itself is divided into multiple stages – N1, N2 and N3. Sleep proceeds in 90-minute cycles of REM and NREM, the order normally being N1 → N2 → N3 → N2 → REM. As humans fall asleep, body activity slows down. Body temperature, heart rate, breathing rate, and energy use all decrease. Brain waves slow down.
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 ...
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Sleeping Girl, Domenico Fetti, c. 1615 . Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. . During sleep, there is a marked decrease in muscle activity and interactions with the surrounding environm
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 ]
[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 ...