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Sleep can follow a physiological or behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone (possibly with some exceptions; see below regarding the sleep of birds and of aquatic mammals), and a compensatory increase following deprivation of the state, this last known ...
They usually do so when the temperature is warmer and will re-emerge in the late summer or early fall. [5] Mosquitoes also are reported to undergo aestivation. [6] False honey ants are well known for being winter active and aestivate in temperate climates. Bogong moths will aestivate over the summer to avoid the heat and lack of food sources. [7]
Due to the difficulty in collecting ejaculate produced during nocturnal emissions, relatively few studies have examined its composition. [4] [5]In the largest study, which included nocturnal emission samples from 10 men with idiopathic anejaculation, the semen concentration was equivalent to samples obtained from the same men by penile vibratory stimulation, although the proportions of sperm ...
The only common observation is that reptiles do not have REM sleep. [7] Sleep in some invertebrates has also been extensively studied, e.g., sleep in fruitflies (Drosophila) [40] and honeybees. [41] Some of the mechanisms of sleep in these animals have been discovered while others remain quite obscure.
[10]: §9.1–2 263–282 (PGO waves have long been measured directly in cats but not in humans because of constraints on experimentation; however, comparable effects have been observed in humans during "phasic" events which occur during REM sleep, and the existence of similar PGO waves is thus inferred.) [15] These waves occur in clusters ...
As professor of sleep medicine Charles Czeisler notes, "the circadian system is set up in a beautiful way to override the homeostatic drive for sleep." [ 1 ] Thus, in many people, there is a dip when the drive for sleep has been building for hours and the drive for wakefulness has not yet started.
The sleep cycle has proven resistant to systematic alteration by drugs. Although some drugs shorten REM periods, they do not abolish the underlying rhythm. Deliberate REM deprivation shortens the cycle temporarily, as the brain moves into REM sleep more readily (the "REM rebound") in an apparent correction for the deprivation. [13]
According to a study on sleep disturbances in the Journal of Neural Transmission, a hypnic jerk occurs during the non-rapid eye movement sleep cycle and is an "abrupt muscle action flexing movement, generalized or partial and asymmetric, which may cause arousal, with an illusion of falling". [13]