Final answer:
The suprachiasmatic nucleus (SCN) regulates the sleep-wake cycle by receiving information from light-sensitive neurons in the retina and controlling the production of melatonin.
Step-by-step explanation:
The suprachiasmatic nucleus (SCN) is located in the hypothalamus and serves as the brain's clock mechanism for regulating the sleep-wake cycle. The SCN receives information from light-sensitive neurons in the retina, which allows it to synchronize the internal clock with the external light-dark cycle. When light stimulates the retinas, a nerve impulse is sent to the SCN, inhibiting the production of melatonin and promoting wakefulness. As light levels decline, melatonin production increases, leading to drowsiness and sleep.