[Function and the mechanism of sleep].
D000818:Animals; D001143:Arousal / Q000502:physiology; D001921:Brain / Q000502:physiology; D002415:Cats; D002940:Circadian Rhythm; D006801:Humans; D007231:Infant, Newborn; D007323:Instinct; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology