AP PSYCHOLOGY

Detailed explanation-1: -Efferent projections from the suprachiasmatic nucleus innervate structures such as the pineal gland, producing melatonin during the night for induction of sleep. Disruptions in the SCN circadian system have been found to correlate with various mood disorders and sleep disorders, detailed in this article.

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: -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).

Detailed explanation-4: -The pineal gland is connected to the central rhythm generator in the suprachiasmatic nucleus (SCN) of the hypothalamus via a multi-synaptic pathway (Figure 3) (Kalsbeek et al., 2006).

Detailed explanation-5: -The amount of melatonin produced depends on the activity of SNAT, which peaks when it is dark outside. Exposure to light induces signals that, as explained earlier, travel from the retina to the suprachiasmatic nucleus and then to the pineal gland, resulting in the degradation of SNAT.