Dictionary of Human Evolution and Biology

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So-called sleep hormone; either of a pair of neuropeptides (A and B) secreted by orexin neurons in the lateral hypothalamus that interact both with feeding centers in the hypothalamus, and with arousal and sleep-wakefulness centres in the brainstem, sympathetic and parasympathetic nuclei, and the limbic system. Orexin neurons are regulated by metabolic cues, including leptin, glucose, and ghrelin. Activation of the orexin neurons apparently contributes to wakefulness, whereas their inactivation permits sleep; mutations or other contributors to inactivation have been linked to narcolepsy. Aka hypocretin(s).

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