Final answer:
The hypothalamus regulates sleep by prompting the pineal gland to increase melatonin production in low light, aligning the sleep-wake cycle with environmental light conditions. The correct option is b.
Step-by-step explanation:
The hypothalamus is involved in sleep regulation primarily through its control of circadian rhythms and its influence on the production of the hormone melatonin. In response to decreasing light, the hypothalamus' suprachiasmatic nucleus (SCN) signals the pineal gland to increase melatonin production, which leads to sleep. This process aligns our sleep-wake cycle with the environmental light-dark cycle. Additionally, the hypothalamus works in conjunction with other brain areas like the thalamus and the pons to control different aspects and stages of sleep.
The hypothalamus is involved in sleep by triggering the pineal gland to produce melatonin in response to decreasing light. The suprachiasmatic nucleus (SCN) in the hypothalamus detects changes in light levels and signals the pineal gland to increase melatonin production, leading to drowsiness and sleep.