A small group of nerve cells in the hypothalamus that express clock proteins, which go through a biochemical cycle of about 24 hours. This sets the pace for daily cycles of activity, sleep, hormone release, and other bodily functions.
An ovoid densely packed collection of small cells of the anterior hypothalamus lying close to the midline in a shallow impression of the optic chiasm. ... (12 Dec 1998) ... 
Type: Term See: anterior hypothalamic area
The main biological clock regulating circadian rhythms of sleep in humans.