Rhodopsin is the primary photoreceptor molecule of vision. Light striking a rhodopsin molecule in a photoreceptor cell of the retina is converted into a biochemical signal by a photochemical reaction. The signal is processed by other cells in the retina and sent to the brain. Two general types of photoreceptor cells exist in the vertebrate retina and are named according to their characteristic shapes: rods and cones. Rod cells are responsible for scotopic or dim-light vision, whereas cone cells are responsible for photopic or bright-light and color vision in vertebrates. Rod cells contain rhodopsin; cone cells contain photopsins, also known as cone pigments or color vision pigments.