Final answer:
Specialized cells in the raphe nuclei produce melatonin, a neurohormone that helps regulate the sleep-wake cycle by increasing production at night and decreasing during the day.
Step-by-step explanation:
The specialized cells in the raphe nuclei sleep system of the pons and medulla are known to produce the neurohormone melatonin. Melatonin is crucial in regulating our sleep-wake cycles, often referred to as our circadian rhythms. The production of melatonin increases during the dark photoperiod, which corresponds to night-time, and decreases with exposure to light during the day. This fluctuation helps signal to our bodies when it is time to sleep or be awake.
The pineal gland, which is influenced by the light-sensitive retinas and the hypothalamus' suprachiasmatic nucleus (SCN), secretes melatonin. As light levels drop in the evening, melatonin production ramps up, leading to increased drowsiness and promoting sleep. Conversely, in response to light, melatonin production wanes, which helps induce wakefulness.