Sleep-wake regulation: arousal systems, sleep architecture and circadian rhythm
The ascending arousal systems, the VLPO flip-flop switch and orexin, REM generation and atonia, the two-process model of adenosine and the suprachiasmatic clock, normal sleep stages and how they change with age, and how these explain narcolepsy, REM sleep behaviour disorder, parasomnias, jet lag and the actions of hypnotics and wake-promoting drugs.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Wakefulness comes from ascending arousal systems: noradrenaline, serotonin, histamine, dopamine, acetylcholine and orexin.
- Sleep comes from GABAergic neurons in the ventrolateral preoptic nucleus (VLPO). VLPO and the monoaminergic and cholinergic arousal nuclei inhibit each other, a flip-flop switch that makes transitions quick. Orexin neurons are not part of that mutual inhibition (VLPO neurons lack orexin receptors); they hold the switch in the wake position by exciting the arousal side.
- Timing follows the two-process model: homeostatic sleep pressure (Process S, adenosine) and the circadian clock in the suprachiasmatic nucleus (Process C).
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Sources
- Principles of Neural Science (6th ed.)McGraw Hill (Kandel, Koester, Mack and Siegelbaum, 2021), 2021
- International Classification of Sleep Disorders, 3rd edition, text revision (ICSD-3-TR)American Academy of Sleep Medicine, 2023
- Saper CB, Scammell TE, Lu J. Hypothalamic regulation of sleep and circadian rhythms. Nature 2005;437:1257-63Nature, 2005
- Postuma RB et al. Risk and predictors of dementia and parkinsonism in idiopathic REM sleep behaviour disorder: a multicentre study. Brain 2019;142:744-59Brain, 2019
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy