Neurobiology of circadian rhythm sleep disorders.

To adapt to a 24-hour environment, nearly all organisms, from mammals to single-celled organisms, have developed endogenous mechanisms that generate nearly 24-hour (circadian) rhythms in physiology and behavior, the most notable being that of the daily cycles of sleep and wake. Disruption of these circadian rhythms is often accompanied by disorders of sleep and wakefulness. With the recent advances in the molecular biology that underlies the development and maintenance of these rhythms, the pathophysiology behind circadian rhythm sleep disorders is becoming better understood.