Background: Sleep problems are a frequent cause for contacting primary care services. Knowledge of basic mechanisms behind sleep and wakefulness is essential for giving adequate information and correct patients' frequent misperception of sleep.
Material and methods: The present review is based on literature identified through a non-systematic search of Pub-med as well as the authors' own research experience.
Results: Sleep need (homeostatic factor), circadian rhythm and behaviour regulate sleepiness, sleep depth and sleep duration. Falling asleep requires central-nervous deactivation. Sleep depth depends on the length of wakefulness beforehand, while duration of sleep mainly depends on timing in relation to the circadian phase of activation. Activation and wakefulness are the combined result of activating several different parts of the brain: thalamus, the reticular activation system, basal forebrain, hypothalamus and monoaminergic cell groups in the brainstem. Falling asleep is a dynamic process and is primarily a consequence of behaviourally induced deactivation. Sleep is especially modulated by GABAergic neurons in the thalamus and basal forebrain, but several neurotransmitters and endogenous substances modulate sleep and wakefulness. Sleep and wakefulness are complex phenomena, and the activity in different brain regions is markedly different depending on whether you are awake or asleep. Hence, a manipulation of these, e.g. by use of certain medications, may cause sleep problems.
Interpretation: Knowledge of sleep is essential for adequate evaluation and treatment of sleep disturbances.