Fig. 2.

The suprachiasmatic nucleus (SCN) as central circadian pacemaker. A) Schematic sagittal view of the location of the human SCN, at the base of the hypothalamus, depicting retinal input from the retinohypothalamic tract (RHT) via the optic nerve, and outputs to neural centers controlling sleep-wake behavior, neuroendocrine and autonomic status. B) Schematic coronal view of mouse SCN to show ventral retinorecipient core and dorsal shell sub-divisions, characterized by their distinction expression of (left) neuropeptides and (right) neurotransmitter receptors, and RHT innervation of SCN core.