visual pigment

physiology

Animals receive light energy by converting it into nerve potentials (electrical potentials) using visual pigments.

The pigment of all animals is thought to consist of a coloured molecule called a chromophore (the carotenoid retinal, also known as retinene) and a protein called an opsin, a medium-sized protein. Vitamin A1 is a component of retinal1; vitamin A2 is a component of retinal2.

There are many types of visual pigments in vertebrates. Scotopsin pigments are associated with seeing in dim light, and in vertebrates, they are found in the rod cells of the retina - the retinal1 forms are called rhodopsins, and the retinal2 forms are called porphyropsins. In vertebrate cone cells, photopsin pigments operate under brighter light than scotopsin pigments; they differ only in their opsin fractions. In the retinal1, iodopsins form; in the retinal2, cyanopsins form.