Figure 42.18 illustrates the events associated with the membrane of a rod cell when light impinges on the it. Rods and cones do not generate APs. The retina of the vertebrate eye consists of several layers of neurons and cells through which the light must pass before impinging on the rods and cones. The ganglion cells are the innermost layer and send the impulses to the CNS via axons in the optic nerve. Ganglion cells do generate action potentials.
Bipolar neurons are the middle layer and the rods and cones are the outermost layer of the retina.
These cells do not generate APs. Neurotransmitters from the rods and cones will influence the bipolar layer which processes the information and passes it on to the ganglion cells, which generate the APs. Figure 42.25 illustrates the pathway of information in the retina. The fovea centralis of the macula lutea receives the most visual information and is primarily made up of cones for color vision and acuity. Moving away from the fovea, the percentage of cones decreases while the percentage of rods increases.