Sleep-wake cycle

The recurring pattern of sleep and wakefulness shaped by circadian timing and accumulated sleep pressure. Its timing and duration emerge from interacting biological processes and environmental cues.

Two-process model of sleep regulation: A model explaining sleep timing through circadian drive and homeostatically accumulated sleep pressure. It directly describes how circadian timing and sleep pressure jointly shape this cycle.
Sleep: A recurring state of reduced responsiveness and altered brain and body activity. It is one of the two broad states whose alternation defines the cycle.
Chronotype: An individual's characteristic tendency toward earlier or later sleep and activity timing. Differences in chronotype shift preferred schedules across the same daily cycle.
Ultradian rhythm: A biological rhythm that repeats more than once within a 24-hour period. Sleep stages cycle within the larger daily sleep-wake pattern.
Circadian rhythm: An approximately 24-hour biological rhythm synchronized by environmental cues, especially light. Its daily timing signal promotes wakefulness or sleep at particular phases.
Wakefulness: A state of consciousness characterized by responsiveness to internal and external stimuli. Its duration and ending are central features of the cycle.
Shift work sleep disorder: A circadian rhythm sleep disorder associated with work schedules that overlap usual sleep times. Misaligned work hours can force wakefulness during the cycle's biological night.
Infradian rhythm: A biological rhythm with a period longer than 24 hours. It contrasts with the approximately daily recurrence of sleep and wakefulness.
Sleep homeostasis: The regulation that increases sleep drive during wakefulness and reduces it during sleep. Its accumulating pressure creates the need for sleep within each recurring cycle.
Sleep architecture: The organization of sleep into recurring stages and cycles across a sleep period. Its changing stages describe the structure within the sleep portion of the cycle.

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