rhodopsin

n. A photoreactive chemical found in retinal rods which changes shape when struck by a photon of appropriate energy and then causes the rod to hyperpolarize, sending an electrical impulse to the nerve and other cells to which it is connected. Chemically it is 11-cis retinal, which changes to all-trans retinal when struck by light. Rhodopsin bleaches out quickly at high ambient brightness levels and is responsible for night vision. Also called visual purple.