AP PSYCHOLOGY

Detailed explanation-1: -It is important to note that “darkness” stimulates the pineal gland to secrete melatonin whereas exposure to light inhibits this mechanism [12].

Detailed explanation-2: -Melatonin secretion is stimulated by darkness and inhibited by light, and in coordination with the SCN, it is centrally involved in maintaining circadian rhythmicity and regulating sleep. The SCN regulates the timing of melatonin release, while melatonin feeds back to the SCN to decrease SCN neuronal firing.

Detailed explanation-3: -The synthesis and release of melatonin are stimulated by darkness, melatonin is the “chemical expression of darkness” and inhibited by light [4].

Detailed explanation-4: -The pineal gland hormone melatonin is released during the biological night and provides the body’s internal biological signal of darkness. Exposure to light both resets the circadian rhythm of melatonin and acutely inhibits melatonin synthesis (1, 2).

Detailed explanation-5: -Darkness prompts the pineal gland to start producing melatonin while light causes that production to stop. As a result, melatonin helps regulate the circadian rhythm and synchronize the sleep-wake cycle with night and day. In doing so, it facilitates a transition to sleep.