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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] Within the sleep of adults and infants there are cyclic fluctuations between quiet and active sleep.
Each sleep cycle lasts about 90 to 110 minutes and includes stages that fall into two main phases: non-REM (or NREM) sleep and REM sleep. Non-REM sleep has three sub-stages: light sleep, deep ...
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The core body and brain temperatures increase during REM sleep and skin ...
REM sleep is decreased during the first half of the sleep period and stage 1 sleep is increased in the second half of the sleep period. [5] Most antidepressants, in particular selective serotonin re-uptake inhibitors (SSRIs), such as citalopram and paroxetine, are potent inhibitors of REM sleep and may also cause a REM rebound on discontinuation.
It is most readily observed in stages of sleep, for example, rapid eye movement sleep (REM) and the delta activity cycle. When awake, brainwaves are faster during the first half of the cycle which corresponds to feeling alert and focused. During the last 20 minutes brainwaves slow and as the body feels dreamy or tired.
NREM, stage 3: deeper sleep. 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 ...
During rest following a sleep-deprived state, there is a period of rebound sleep which has longer and deeper episodes of SWS to make up for the lack of sleep. [6] On a hypnogram, a sleep cycle is usually around 90 minutes and there are four to six cycles of REM/NREM stages that occur during a major period of sleep.
Mammalian sleep can be sub-divided into two distinct phases - REM (rapid eye movement) and non-REM (NREM) sleep. In humans and cats, NREM sleep has four stages, where the third and fourth stages are considered slow-wave sleep (SWS). SWS is considered deep sleep, when metabolism is least active. [1]