Endogenous and exogenous factors on sleep-wake cycle regulation.

A number of theories have proposed the involvement of different brain structures and neurotransmitters in order to explain the regulation of the sleep wake cycle. However, there is no clear consensus as to the mechanisms through which the brain structures and their various neurotransmitters interact to produce theses phases. Perhaps the problem is related to the fact sleep is a very fragile state, easily modified or influenced by a variety of substances or experimental manipulations. In this paper, we describe the evidence of two different groups of factors that induce important changes on the sleep wake cycle. The endogenous factors: neurotransmitters; hormone; peptides; and some substances of lipidic nature and exogenous factors: stress, food intake, learning, sleep deprivation, sensorial stimulation, exercise and temperature on the regulation the sleep-wake cycle. Likewise, we propose a hypothesis which attempts to reconcile the fact that endogenous and exogenous factors have similar effects.