circadian pacemakerA cluster of hypothalamic neurons, the activity of which fluctuates in ± 24-hour cycles, resides in the pineal gland—an aggregate of parenchymal cells surrounded by a neuroglial network with direct retinal innervation (retinohypothalamic tract), which is thought to act by secreting melatonin at night—weighs 100–180 mg, and derives embryologically from the ependyma at the roof of the third ventricle. In rats, the biogenic oscillator/internal clock resides in the ventral hypothalamus; in hamsters, in the suprachiasmatic nucleus. The circadian pacemaker influences the pineal gland.
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circadian pacemakerA cluster of neurons, the activity of which fluctuates in ± 24 hr cycles; the CP resides in the pineal gland, weighs 100-180 mg, and derives embryologically from the ependyma at the roof of the 3rd ventricle; the CP influences the pineal gland, which produces melatonin at night. See Bright light therapy, Chronotherapy, Circadian rhythm, Melatonin, Seasonal affective disorder, Zeitgeber.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.