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Sleep is defined by reduced activity and altered consciousness, with inhibited sensory processing and decreased muscle activity.
Sleep is a naturally recurring state of reduced mental and physical activity in which consciousness is altered and sensory responsiveness is inhibited. Compared with wakefulness, sleepers react less to stimuli, yet sleep is not “inactive”—it involves active brain patterns and is more organized than states such as coma or disorders of consciousness. During sleep, muscle activity decreases and interactions with the surrounding environment are reduced. A core characteristic of sleep is that it occurs in repeating cycles in which the body alternates between two distinct modes: non-REM (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep typically occurs first and includes slow-wave (deep) sleep, when heart rate and body temperature fall and the brain uses less energy. REM sleep, which makes up a smaller portion of total sleep time, is strongly associated with dreaming and features desynchronized, fast brain activity, eye movements, reduced muscle tone, and changes in physiological regulation. Sleep is also regulated by internal timing systems and measurable physiological changes. The circadian clock promotes sleep at night, largely through light-driven hormonal signaling (including melatonin), while sleep-wake homeostasis (“sleep debt”) increases the drive to sleep the longer one stays awake. Researchers monitor sleep using tools such as EEG (brain waves), EOG (eye movements), and EMG (muscle activity), often combined as polysomnography.
Sleep is defined by reduced activity and altered consciousness, with inhibited sensory processing and decreased muscle activity.
Sleep cycles alternate between NREM and REM, with NREM including slow-wave (deep) sleep and REM linked to dreaming and characteristic brain/eye/muscle changes.
Sleep timing is governed by circadian rhythms (light/hormones) and homeostatic sleep pressure (sleep debt), and sleep stages can be measured using EEG/EOG/EMG (polysomnography).
Sleep is a state of reduced mental and physical activity with altered consciousness and inhibited sensory activity.
NREM sleep is the first major sleep mode, including slow-wave (deep) sleep with reduced energy use and lowered heart rate and body temperature.
REM sleep is a distinct sleep mode characterized by rapid eye movements, desynchronized fast brain waves, reduced muscle tone, and frequent dreaming.
A repeating sequence of NREM and REM stages that typically lasts about 90 minutes per cycle.
The internal timing system that uses environmental cues (especially light) to promote sleep at appropriate times, largely via melatonin regulation.
The mechanism that increases the drive to sleep the longer an organism stays awake, contributing to sleep debt.
A sleep study that simultaneously records EEG, EOG, and EMG to measure sleep stages and physiological changes.
Electrical activity patterns measured by EEG whose frequency and amplitude vary across sleep and wake stages.
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