The primary circadian "clock" in mammals is located in the suprachiasmatic nucleus (or nuclei) (SCN), a pair of distinct groups of cells located in the hypothalamus. Destruction of the SCN results in the complete absence of a regular sleep–wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eye contains "classical" photoreceptors ("rods" and "cones"), which are used for conventional vision. But the retina also contains specialized ganglion cells that are directly photosensitive, and project directly to the SCN, where they help in the entrainment (synchronization) of this master circadian clock. COUNT 5
QSN1 Where is the primary circadian gene located in humans? ANS1 suprachiasmatic nucleus QSN2 Where are these cell groups found in humans? ANS2 hypothalamus QSN3 What would the loss of the SCN cells cause in the sleep-wake rhythm? ANS3 complete absence QSN4 What provides information to the SCN? ANS4 eyes QSN5 What special cells in the eyes communicate directly to the SCN cells? ANS5 ganglion