Pineal Gland
About the Pineal Gland
The pineal gland is a small pea sized organ approximately 5 to 8 mm near the center of the brain, behind the third ventricle. It produces melatonin from serotonin, regulated by light exposure via the retinohypothalamic tract to the suprachiasmatic nucleus SCN and sympathetic nervous system. Melatonin secretion peaks at night around 2 to 4 AM and is suppressed by light, particularly blue light. It signals nighttime and helps regulate the sleep wake circadian rhythm. The pineal calcifies with age, producing pineal sands corpora arenacea visible on X-ray and used as a midline marker. Pineal tumors cause Parinaud syndrome vertical gaze palsy due to compression of the dorsal midbrain. Melatonin has been studied in circadian rhythm disorders such as jet lag and delayed sleep phase syndrome. The French philosopher Rene Descartes famously described the pineal gland as the seat of the soul.
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