Each of a pair of small nuclei in the hypothalamus of the brain, above the optic chiasma, thought to be concerned with the regulation of physiological circadian rhythms.
- In mammals it responds indirectly to light because it receives messages along fibres from nerve cells of the suprachiasmatic nucleus of the hypothalamus, which themselves receive signals from the eye via fibres of the optic nerve.
- The clock, which is located in the brain in the suprachiasmatic nucleus of the hypothalamus, programs daily cyclic changes in the body, thereby creating two distinct periods, a biological day and a biological night.
- Within mammals a region of the hypothalamus known as the suprachiasmatic nucleus acts as a central clock regulating rhythms throughout the rest of the body.
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Syllabification: su·pra·chi·as·mat·ic nu·cle·us
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