Genes that regulated biological rhythms have been isolated. Interactions between sleep and all other body systems have been determined. Sleep affects the respiratory, cardiovascular, endocrine and neurological systems. Some ways in which these systems are affected include, but are not limited to: melatonin, cortisol and growth hormone secretion; regulation of core body temperature; and immune function.
Sleep is Regulated by Two Simultaneous Processes:
• Homeostatic Mechanism
• Circadian Rhythm
The homeostatic mechanism is an individual’s “sleep drive.” This urge to sleep is dependent upon time spent awake, quantity and quality of previous sleep and a person’s sleep needs.
The circadian rhythm is a 24-hour biological clock of sleep and wakefulness. Humans tend to alternate between periods of wakefulness lasting about 16 hours. Light helps synchronize rhythms with the cycles of the sun and moon by sending a retinal signal, melanoposin, to the hypothalamic suprachiasmatic nucleus. The supraschiasmatic nucleus is a network of brain cells and genes that act as pacemakers to control circadian time functions.