Which hormone influences the sleep-wake cycles by regulating light exposure?

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

Answer: (B)

Melatonin is the hormone that plays a crucial role in regulating sleep-wake cycles, especially in response to light exposure. It is produced by the pineal gland in the brain, and its secretion is influenced significantly by the amount of light present in the environment.

When it is dark, the body produces more melatonin, signaling to the body that it is time to sleep. Conversely, when light exposure increases, melatonin production decreases, helping to promote wakefulness. This process is closely linked to the circadian rhythms, which are natural, internal processes that follow a roughly 24-hour cycle and regulate various biological functions, including sleep patterns.

In contrast, cortisol is associated with stress response and energy metabolism but is not directly involved in regulating sleep cycles. Serotonin does influence mood and can affect sleep indirectly, but its primary roles are in mood stabilization and processing of information. Adrenaline is primarily involved in the body’s fight-or-flight response and does not have a direct function in sleep-wake regulation. Thus, melatonin is clearly the hormone that most directly affects sleep-wake cycles through its response to light exposure.