Sleep homeostasis

Homesostatic sleep pressure

Homeostasis, refers to any internal biochemical system that regulates the body’s internal environment, with a view to maintaining properties such as temperature, acidity, etc, in a stable and relatively constant condition.

Sleep-wake homeostasis, refers to a kind of internal timer or counter that generates a homeostatic sleep drive or pressure for sleep as a function of the amount of time elapsed since the last adequate sleep episode.

The longer one is awake, the stronger the desire and need to sleep becomes.

The longer one is awake the greater the likelihood of falling asleep.

The longer one has been asleep, the more the pressure for sleep to dissipate, and the greater the likelihood of awakening.

Endogenous sleep-regulating substance, or substances, builds up in the CSF during our waking hours, increasing the pressure to sleep as it accumulates.

This pressure to sleep is released by the act of sleeping itself, during which the levels of the sleep-regulating substance in the body rapidly declines.

Adenosine is a neuromodulator in the brain, and has the effect of inhibiting many of the bodily processes associated with wakefulness, particularly those involving the neurotransmitters norepinephrine, acetylcholine and serotonin.

Adenosine levels in the basal forebrain rise as sleep debt builds up, and then fall rapidly during the subsequent sleep period.

Adenosine is created over the course of the day.

Adenosine, the natural by-product of using up our internal energy stores.

Adenosine forms the core of adenosine triphosphate (ATP), which is the energy-storage molecule that powers most of the biochemical reactions inside cell.

The body’s regular desire for sleep stems, at least in part, from the brain’s periodic need to replenish low stores of energy.

The brain’s glycogen energy stores are depleted throughout the day, resulting in the extra-cellular adenosine build up of adenosine.

During sleep, the adenosine is removed and replaced by new glycogen.

Adenosine, is the best-known of the sleep-regulating substances involved in the homesostatic sleep drive.

High levels of adenosine lead to sleepiness.

Commonly used stimulants caffeine in coffee, tea, cola and energy drinks, theophylline in tea and chocolate, work as adenosine antagonists or receptor blockers, inhibiting or dampening its sleepiness effect, and thereby maintaining alertness.

The main sleep-wake homeostatic mechanism appears as non-REM sleep, and particularly deep or slow-wave sleep.

The pressure to sleep is to enter into deep non-REM sleep, a pressure that is only relieved by a period of actual deep non-REM sleep.

The loss of REM sleep leads to an increase in the tendency to enter REM sleep.

On awakening in the morning, sleep inertia sometimes occurs manifesting as grogginess and impaired motor activity which may last for up to half-an-hour after waking, and is most likely to occur when waking from deep slow-wave sleep rather than from light sleep or REM sleep.

Sleep inertia may be more severe and longer lasting after waking from a sleep period or nap following a prolonged period of wakefulness or accumulated sleep debt.

Sleep inertia may be caused by an excessive build-up of adenosine through the normal sleep-wake homeostasis process that has not fully dissipated by awakening time.

Light exposure directly affect alertness, performance and mood through the sleep-wake homeostatic process, in addition to its essential part in regulating the circadian clock.

A longer duration of sleep greater than 10 hours per day is significantly associated with increased overall mortality, including coronary heart disease and cancer related mortality.

Sleep duration of less than 10 hours versus less than eight hours is associated with a 32% higher all-cause mortality, 40% higher coronary heart disease, and a 45% higher cancer related mortality.

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