ABSTRACT
When light strikes a vertebrate retinal photoreceptor, its internal electrical potential, when referenced to the space outside of it, becomes more negative-it hyperpolarizes. When a photoreceptor hyperpolarizes, it signals the occurrence of light to secondary neurons. The vertebrate photoreceptor is unusual because most neurons signal by depolarizing-their internal potentials become more positive. Indeed, hyperpolarization to light sets the vertebrate photoreceptor apart from photoreceptors of invertebrates, from photoreceptors in the “3rd” (parietal) eye of some vertebrates, and from photosensitive ganglion cells in vertebrate retinas, all of which depolarize to light.
