The hypothalamus is a part of the brain containing a number of nuclei with a variety of functions. It is central in the regulation of hormone secretion, sleep, and circadian functions. The suprachiasmatic nucleus of the hypothalamus is a key component in controlling circadian rhythms and generates the rhythm of melatonin secretion from the pineal gland and cortisol secretion. Both melatonin and cortisol are involved in the regulation of circadian rhythms and sleep.