Circadian rhythm is an internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours. It influences physical, mental, and behavioral changes according to the light and darkness in an organism's environment.
A hormone produced by the pineal gland during the night that regulates sleep patterns.
Suprachiasmatic Nucleus (SCN): An area of the brain in the hypothalamus responsible for controlling circadian rhythms by signaling other parts of the brain and body.
Sleep: Wake Cycle - The cycle of alternating states of sleep and wakefulness reflecting both circadian rhythms and homeostasis