Sleep and wakefulness are a manifestation of circadian rhythms.
Active life and interaction with the outside world occurs during wakefulness, and sleep ensures the restoration of working capacity, processing and assimilation of the information received.
In order for the state of sleep to arise, a number of special substances are produced in the brain (for example, serotonin, produced by neurons in the central part of the midbrain).
Sleep is a special state of the brain and the whole organism as a whole, characterized by muscle relaxation, a weak reaction to external stimuli.
Sleep is a state of oppression of consciousness and a weakening of human ties with the environment.
Sleep is a cyclical phenomenon. A typical 7-8 hour sleep consists of 4-5 cycles, regularly replacing each other. Each cycle includes two phases: NREM sleep and REM sleep.
Immediately after falling asleep, slow (or deep, or slow-wave) sleep develops. It is accompanied by a decrease in breathing and pulse, muscle relaxation. During deep, slow wave sleep, the rhythmic activity of the brain, metabolism and body temperature decrease.
After 1–1.5 hours, slow sleep is replaced by rapid (or superficial, or fast-wave). In this phase, the activity of all internal organs is activated, breathing becomes frequent, deep, the work of the heart intensifies, metabolism increases, rapid eye movements, contractions of facial muscles, finger movements are observed, sometimes the sleeper begins to speak. In this phase, a person sees dreams.
Dreaming is the subjective perception of images (visual, auditory, tactile, gustatory and olfactory) that arise in the mind of a sleeping person.
IM Sechenov called dreams “unprecedented combinations of experienced impressions.”
REM sleep lasts 10-15 minutes. After it, a new cycle of slow sleep begins. By the morning, the duration of REM sleep increases to 25-30 minutes (an increase in the duration of REM sleep is important for activating body functions by the time of awakening).