In the human eye, three types of specialized ganglion cells transmit electrical impulses to the brain. Among these three cell populations are rod and cone cells, which participate in the photo-transduction step of light perception, along with other light sensitive ganglion cells. It is a system whereby the photosensitive pigment rhodopsin (or one of its analogs) rearranges in response to light, and this change in chemical structure fires electrical impulses to the brain which in turn interprets the incoming impulses as a visual image.