The gland that regulates sleep cycles is the:

• A. Pineal gland
• B. Pituitary gland
• C. Thalamus
• D. Cerebellum

Answer: (A)

Sleep-wake cycles are coordinated by hormones linked to our internal clock. The pineal gland produces melatonin, a hormone that helps promote sleep. The brain’s circadian clock (the clock in the hypothalamus, driven by signals from the retina about light and dark) tells the pineal gland when to release melatonin—more at night and less during the day—so melatonin helps push us toward sleep as darkness falls and wakefulness during daylight returns. The pituitary gland regulates many other hormones, not the timing of sleep. The thalamus is important for consciousness and sleep stages but isn’t a gland that secretes sleep-regulating hormones. The cerebellum coordinates movement and balance, not sleep regulation.