Which brain region acts as the master clock coordinating circadian rhythms?

Which brain region acts as the master clock coordinating circadian rhythms?

• A. Pineal Gland
• B. Thalamus
• C. Hippocampus
• D. Suprachiasmatic Nucleus

Answer: (D)

Circadian rhythms are timed by a central clock that keeps the body's 24-hour cycle aligned with day and night. The brain region that serves as this master clock is in the hypothalamus, just above the optic chiasm, and is called the suprachiasmatic nucleus. It gets direct light information from the eyes through special retinal cells that contain melanopsin, which helps reset the clock daily to match the external light-dark cycle. Once set, the SCN coordinates downstream rhythms by sending signals to other brain areas and the endocrine system, including controlling the pineal gland’s production of melatonin in response to darkness. The pineal gland itself isn’t the clock; it acts as an output organ that translates SCN timing into melatonin release. The thalamus and hippocampus aren’t pace-makers for circadian rhythms—the thalamus relays sensory information, and the hippocampus is key for memory. So, the region that coordinates circadian timing is the suprachiasmatic nucleus.

Circadian rhythms are timed by a central clock that keeps the body's 24-hour cycle aligned with day and night. The brain region that serves as this master clock is in the hypothalamus, just above the optic chiasm, and is called the suprachiasmatic nucleus. It gets direct light information from the eyes through special retinal cells that contain melanopsin, which helps reset the clock daily to match the external light-dark cycle. Once set, the SCN coordinates downstream rhythms by sending signals to other brain areas and the endocrine system, including controlling the pineal gland’s production of melatonin in response to darkness. The pineal gland itself isn’t the clock; it acts as an output organ that translates SCN timing into melatonin release. The thalamus and hippocampus aren’t pace-makers for circadian rhythms—the thalamus relays sensory information, and the hippocampus is key for memory. So, the region that coordinates circadian timing is the suprachiasmatic nucleus.