Photoreceptors in the retina
The retina is the light-sensitive cell layer at the back of the eye. Its rod and cone photoreceptors provide information about light intensity and, in the case of cones, the wavelength of visible light.
Rod cells
Rod cells are particularly important for detecting light intensity. They occur across the retina, with their highest density outside the fovea.
Cone cells
Cone cells provide information about different wavelengths of visible light and occur at their greatest concentration in the fovea.
Converting light into an electrical response
Rod and cone cells contain optical pigments. Light alters these pigments, beginning the electrical response of the photoreceptor.
- Light causes chemical breakdown of an optical pigment inside a rod or cone cell.
- The pigment change leads to a generator potential.
- If the generator potential is large enough, a nerve impulse is transmitted through a bipolar neurone.
- Visual information ultimately passes along the optic nerve to the brain.