Functions of sleep

Extremely, the function of sleep is not known. Between the numerous ideas which have been proposed two have emerged as front runners the metabolic hypothesis and the memory hypothesis.

The metabolic hypothesis postulates which NREM sleep gives a period of low metabolic demand required to replenish neural energy resources depleted during waking.  One option is that wakefulness decreases the ATP: AMP ratio resulting in addition of extracellular adenosine that, acting by adenosine A1 receptors inhibits lowers brain metabolic demand and neuronal activity. Although, the requirement for NREM sleep seems to extend way beyond the nervous system. The Sleep-deprived rats suffer anorexia (even though their food intake increases), lose the ability to thermoregulate, and die as a consequence of immune system failure after about four weeks.  Since, sleep may have global anabolic functions which conserve energy stores and core temperature. Circumstantial evidence for this involves:

- Smaller mammals with the highest metabolic rates sleep the most.

- Heat stress or experimental warming of the pre-optic hypothalamus that is involved in both thermoregulation and triggering NREM sleep can trigger or prolong NREM sleep.