Final answer:
Retinal ganglion cells containing the photopigment melanopsin are sensitive to light and help regulate circadian rhythms by sending signals to the suprachiasmatic nucleus of the hypothalamus.
Step-by-step explanation:
Some ganglion cells of the retina contain a photopigment called melanopsin that is sensitive to luminance and helps the hypothalamus regulate circadian rhythms. These cells project from the optic chiasm to the suprachiasmatic nucleus (SCN) of the hypothalamus. They are sensitive to the presence or absence of light, but unlike photoreceptors, they do not contribute to image formation. Instead, these retinal ganglion cells (RGCs) play a crucial role in the synchronization of our circadian rhythms by transmitting information about light and darkness to the SCN, which acts as the body's internal clock.