Final answer:
The retinohypothalamic pathway connects the retina to the suprachiasmatic nucleus of the hypothalamus, which then regulates melatonin production by the pineal gland.
Step-by-step explanation:
The retinohypothalamic pathway consists of axons that project from the retina to the suprachiasmatic nucleus (SCN) of the hypothalamus, which indirectly controls the production of the hormone melatonin by the pineal gland. The SCN serves as the body's internal clock, regulating our circadian rhythms, including sleep/wake patterns. As it receives input about light levels from the retina, the SCN adjusts the production of melatonin, which is crucial for sleep regulation. The pathway is instrumental in synchronizing the body's circadian rhythms with the external environment.