Which hormone is involved in the regulation of the sleep-wake cycle?

• A. Cortisol
• B. Serotonin
• C. Melatonin
• D. Testosterone

Answer: (C)

Melatonin is a hormone that plays a crucial role in regulating the sleep-wake cycle, also known as the circadian rhythm. It is produced by the pineal gland in response to darkness, signaling to the body that it is time to sleep. This hormone helps to induce sleepiness and lower alertness at night, while its secretion decreases in response to light, promoting wakefulness during the day.

Cortisol, although important for various bodily functions, is more associated with stress responses and is generally higher in the morning to help wake the body up. Serotonin is a neurotransmitter that can influence mood and sleep, but it does not directly regulate the sleep-wake cycle like melatonin does. Testosterone is primarily associated with reproductive functions and does not have a direct impact on sleep regulation.