Sleep homeostasis

Sleep homeostasis is the regulation of sleep pressure: it rises during wakefulness and falls during sleep. It helps determine when sleep begins and how intense it is.

Adenosine: A neuromodulator that accumulates in the brain during wakefulness and inhibits neural activity through specific receptors. Its accumulation during prolonged wakefulness is one proposed source of rising sleep pressure.
Process S: The homeostatic component of the two-process model of sleep regulation, rising during wake and declining during sleep. It formalizes the pressure described by sleep homeostasis.
Nathaniel Kleitman: A physiologist whose research helped establish sleep science as an experimental field in the twentieth century. His work on sleep and biological rhythms shaped the research context for homeostatic models.
Caffeine: A stimulant that blocks adenosine receptors and can temporarily reduce sleepiness. It masks some effects of rising pressure without removing the underlying need for sleep.
Adenosine hypothesis of sleep: The hypothesis that rising adenosine signaling during wakefulness contributes to sleep pressure and sleep initiation. It offers a biochemical account, but does not fully explain homeostatic regulation.
Sleep–wake cycle: The recurring alternation between sleep and wakefulness, shaped by homeostatic pressure and circadian timing. Homeostatic pressure helps set sleep timing alongside the circadian system.
Two-process model of sleep regulation: A model in which sleep timing reflects the interaction of homeostatic Process S and circadian Process C. It places sleep pressure within a framework that also accounts for daily timing.
Alexander Borbély: A Swiss sleep researcher who developed the two-process model of sleep regulation. His model gave sleep homeostasis its influential mathematical formulation.
Napping: A short sleep episode taken outside the main sleep period. A nap can reduce accumulated pressure and alter sleepiness later in the day.
Glymphatic system: A proposed brain-wide pathway for fluid exchange and waste clearance, described as more active during sleep. Its relationship to sleep need is debated and does not establish a complete pressure mechanism.

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