AP PSYCHOLOGY

Detailed explanation-1: -Its major tract is the retinohypothalamic tract originating from photosensitive ganglion cells of the retina. Efferent projections from the suprachiasmatic nucleus innervate structures such as the pineal gland, producing melatonin during the night for induction of sleep.

Detailed explanation-2: -The suprachiasmatic nucleus, via an inhibitory projection to the paraventricular nucleus of the hypothalamus, controls the sympathetic output to the pineal gland that is responsible for melatonin secretion. This pathway is responsible for the peak of melatonin secretion during darkness.

Detailed explanation-3: -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.

Detailed explanation-4: -Light exposure is the most important factor related to pineal gland function and melatonin secretion. A single daily light pulse of suitable intensity and duration in otherwise constant darkness is enough to phase shift and to synchronize the melatonin rhythm to 24h (16).