Final answer:
Light inhibits the pineal gland by decreasing the production of melatonin, which controls the circadian rhythms and sleep-wake cycle.
Step-by-step explanation:
The pineal gland is inhibited by exposure to light, which reduces the production of the hormone melatonin. Melatonin is responsible for controlling our circadian rhythms, which includes the sleep-wake cycle. The process starts when light detected by the retina sends a signal to the suprachiasmatic nucleus (SCN) in the hypothalamus. The SCN then signals the pineal gland to decrease melatonin production, promoting wakefulness. Conversely, when there is a lack of light, such as at night, melatonin production increases, which leads to drowsiness and prepares the body for sleep. While melatonin is known for regulating sleep, it also has an inhibitory effect on reproductive functions and acts as an antioxidant, protecting the central nervous system from harmful free radicals.