Which brain structure houses the master circadian clock?

Which brain structure houses the master circadian clock?

• A. Pineal gland
• B. Suprachiasmatic nucleus
• C. Hippocampus
• D. Amygdala

Answer: (B)

The master circadian clock is housed in the suprachiasmatic nucleus of the hypothalamus. This small cluster of neurons generates the body’s internal 24-hour rhythms and sets the timing by aligning them to the day-night cycle. It receives direct light information from the retina through the retinohypothalamic pathway, using this input to synchronize the clock with external environmental cues. Once the SCN sets the pace, it communicates with other brain regions and with the pineal gland to adjust hormonal signals, particularly melatonin, which promotes sleepiness at night. The pineal gland isn’t the clock itself; it acts downstream to regulate sleepiness in response to the SCN’s timing. The hippocampus and amygdala handle memory and emotion, not circadian timing.

The master circadian clock is housed in the suprachiasmatic nucleus of the hypothalamus. This small cluster of neurons generates the body’s internal 24-hour rhythms and sets the timing by aligning them to the day-night cycle. It receives direct light information from the retina through the retinohypothalamic pathway, using this input to synchronize the clock with external environmental cues. Once the SCN sets the pace, it communicates with other brain regions and with the pineal gland to adjust hormonal signals, particularly melatonin, which promotes sleepiness at night. The pineal gland isn’t the clock itself; it acts downstream to regulate sleepiness in response to the SCN’s timing. The hippocampus and amygdala handle memory and emotion, not circadian timing.