Context: 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.

Question: Where is the primary circadian gene located in humans?
Answer: suprachiasmatic nucleus

Question: Where are these cell groups found in humans?
Answer: hypothalamus

Question: What would the loss of the SCN cells cause in the sleep-wake rhythm?
Answer: complete absence

Question: What provides information to the SCN?
Answer: eyes

Question: What special cells in the eyes communicate directly to the SCN cells?
Answer: ganglion

Question: Where is the secondary circadian clocl located?
Answer: Unanswerable

Question: What surrounds the hypothalamus?
Answer: Unanswerable

Question: What do the SCN cells cause in the sleep-wake rythem?
Answer: Unanswerable

Question: What do the SCN recieve through the skin?
Answer: Unanswerable

Question: What does the pupil contain that are directly photosensative?
Answer: Unanswerable