Sleep

sleepingsleep architectureasleepsleep stagessleep patternsstages of sleepsleep patternsoporificWaking uprest
Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles during rapid eye movement (REM) sleep, and reduced interactions with surroundings.wikipedia
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Rapid eye movement sleep

REM sleepREMrapid eye movement
Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles during rapid eye movement (REM) sleep, and reduced interactions with surroundings. Sleep occurs in repeating periods, in which the body alternates between two distinct modes: REM sleep and non-REM sleep.
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, distinguishable by random/rapid movement of the eyes, accompanied with low muscle tone throughout the body, and the propensity of the sleeper to dream vividly.

Sleep cycle

cycling of the sleep stagesrepeating periodssleep cycles
Sleep occurs in repeating periods, in which the body alternates between two distinct modes: REM sleep and non-REM sleep.
The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep.

Sleep disorder

sleep disorderssleep disturbancesleep disturbances
Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia, narcolepsy, and sleep apnea; parasomnias such as sleepwalking and REM behavior disorder; bruxism; and circadian rhythm sleep disorders.
A sleep disorder, or somnipathy, is a medical disorder of the sleep patterns of a person or animal.

Insomnia

trouble sleepingsleeplessnessdifficulty sleeping
Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia, narcolepsy, and sleep apnea; parasomnias such as sleepwalking and REM behavior disorder; bruxism; and circadian rhythm sleep disorders.
Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping.

Wakefulness

awakeawakeningwaking
It is distinguished from wakefulness by a decreased ability to react to stimuli, but more reactive than coma or disorders of consciousness, with sleep displaying very different and active brain patterns.
Being awake is the opposite of the state of being asleep in which most external inputs to the brain are excluded from neural processing.

Sleep apnea

sleep apnoeaobstructive sleep apneasleep apnea syndromes
Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia, narcolepsy, and sleep apnea; parasomnias such as sleepwalking and REM behavior disorder; bruxism; and circadian rhythm sleep disorders.
Sleep apnea, also spelled sleep apnoea, is a sleep disorder where a person has pauses in breathing or periods of shallow breathing during sleep.

Narcolepsy

narcolepticdifficulty in controlling her sleepdifficulty staying awake
Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia, narcolepsy, and sleep apnea; parasomnias such as sleepwalking and REM behavior disorder; bruxism; and circadian rhythm sleep disorders.
People with narcolepsy tend to sleep about the same number of hours per day as people without, but the quality of sleep tends to be worse.

Sleep medicine

sleep laboratorysleep managementsleep specialist
Simultaneous collection of these measurements is called polysomnography, and can be performed in a specialized sleep laboratory.
Sleep medicine is a medical specialty or subspecialty devoted to the diagnosis and therapy of sleep disturbances and disorders.

Dream

dreamsdreamlikedreaming
A well-known feature of sleep is the dream, an experience typically recounted in narrative form, which resembles waking life while in progress, but which usually can later be distinguished as fantasy. It is the main occasion for dreams (or nightmares), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis.
A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep.

Non-rapid eye movement sleep

NREMNREM sleepnon-REM sleep
Sleep occurs in repeating periods, in which the body alternates between two distinct modes: REM sleep and non-REM sleep.
Non-rapid eye movement sleep (NREM), also known as quiescent sleep, is, collectively, sleep stages 1–3, previously known as stages 1–4.

Polysomnography

polysomnogramsleep studypolysomnographic
Simultaneous collection of these measurements is called polysomnography, and can be performed in a specialized sleep laboratory.
Polysomnography (PSG), a type of sleep study, is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine.

Sleep inertia

grogginessgroggy
Scientific studies on sleep have shown that sleep stage at awakening is an important factor in amplifying sleep inertia.
It persists during the transition of sleep to wakefulness, where an individual will experience feelings of drowsiness, disorientation and a decline in motor dexterity.

Thalamus

thalamicMetathalamusthalami
Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex.
The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter in the dorsal part of the diencephalon of the brain with several functions such as relaying of sensory signals, including motor signals to the cerebral cortex, and the regulation of consciousness, sleep, and alertness.

Free-running sleep

free-runningfree runningfree running period
Scientists refer to such conditions as free-running of the circadian rhythm.
Free-running sleep is a sleep pattern that is not adjusted (entrained) to the 24-hour cycle in nature nor to any artificial cycle.

Nightmare

nightmaresnightmarishbad dreams
It is the main occasion for dreams (or nightmares), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis.
After a nightmare, a person will often awaken in a state of distress and may be unable to return to sleep for a short period of time.

Hormone

hormoneshormonalprohormone
Sleep timing depends greatly on hormonal signals from the circadian clock, or Process C, a complex neurochemical system which uses signals from an organism's environment to recreate an internal day–night rhythm.
Hormones serve to communicate between organs and tissues for physiological regulation and behavioral activities such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress induction, growth and development, movement, reproduction, and mood manipulation.

Pineal gland

pineal foramenpinealpineal body
The circadian pacemaker in the suprachiasmatic nucleus has a direct neural connection to the pineal gland, which releases the hormone melatonin at night.
The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles.

Sleep deprivation

deprived of sleepsleep deprivedlack of sleep
Induced or perceived lack of sleep is called sleep deprivation.
Sleep deprivation, also known as insufficient sleep or sleeplessness, is the condition of not having enough sleep.

Diurnality

diurnaldiurnal activityactive during the day
Process C counteracts the homeostatic drive for sleep during the day (in diurnal animals) and augments it at night.
Diurnality is a form of plant or animal behavior characterized by activity during daytime, with a period of sleeping or other inactivity at night.

Cortisol awakening response

peak in the awakening hourscortisol
Cortisol levels typically rise throughout the night, peak in the awakening hours, and diminish during the day.

Electroencephalography

EEGelectroencephalogramelectroencephalograph
Key physiological methods for monitoring and measuring changes during sleep include electroencephalography (EEG) of brain waves, electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity.
Several of these oscillations have characteristic frequency ranges, spatial distributions and are associated with different states of brain functioning (e.g., waking and the various sleep stages).

Sleep state misperception

are not aware of itParadoxical insomnia
Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy, and those affected with sleep state misperception may typically report having slept only four hours despite having slept a full eight hours.
Sleep state misperception (SSM) is a term in the International Classification of Sleep Disorders (ICSD) most commonly used for people who mistakenly perceive their sleep as wakefulness, though it has been proposed that it be applied to those who severely overestimate their sleep time as well ("positive" sleep state misperception).

Consciousness

consciousconsciouslyhuman consciousness
Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles during rapid eye movement (REM) sleep, and reduced interactions with surroundings.
The two most widely accepted altered states are sleep and dreaming.

Siesta

afternoon sleepmidday napsleeping
The siesta habit has recently been associated with a 37% lower coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep.
Such a period of sleep is a common tradition in some countries, particularly those where the weather is warm.

Caffeine

caffeinatedHealth effects of caffeineNo-Doz
Coffee and caffeine temporarily block the effect of adenosine, prolong sleep latency, and reduce total sleep time and quality.
Caffeine can delay or prevent sleep and improves task performance during sleep deprivation.