The visual pathway in the retina consists of a chain of different nerve cells. Light first travels through all the layers until it reaches the photoreceptor layer, the rod and cone layer. Rods and cones use photopigments, which contain opsin and a chromophore, to help them convert light into energy. This energy is then passed on to the horizontal and bipolar cells. Horizontal cells prevent the hyperpolarization of peripheral rods and cones if needed, and they receive color-coded signals from cones that they then continue along the optic pathway. Bipolar cells can be divided into rod bipolar cells and cone bipolar cells. Cone bipolar cells can be further subdivided into midget cone bipolar cells, which only contact one cone cell and one ganglion, and diffuse cone bipolar cells, which can contact several cone and ganglion cells. Bipolar cells can either hyperpolarize or depolarize with light, and they pass their signal on to amacrine cells or ganglion cells. Amacrine cells provide inhibition to the visual pathway, either through feedback inhibition on the bipolar cells or feedforward inhibition on ganglion cells. A1 amacrine cells provide long-range inhibition of ganglion cells. Indoleamine-accumulating amacrine cells provide a reciprocal response to bipolar cells, preventing them from hyperpolarizing so that their signal does not continue. AII amacrine cells receive input from bipolar cells and output the signal to different bipolar cells to be transmitted to ganglion cells. Ganglion cells, the last nerve cells in the visual pathway, only receive input when light hits the part of the receptive zone that produces a discharge when stimulated by a light source. Ganglion cells are specialized to detect movement in a specific direction. This prevents the brain from receiving unnecessary information. EphrinA and EphrinB are two molecules that form gradients that lead the ganglion cells to their specific destination in the brain. Magnocellular (MC) ganglion cells and intrinsically photosentive retinal ganglion cells (ipRGCs) are specific types of ganglion cells, with MC cells dominating during fixational eye movements, and ipRGCs working as circadian photoreceptors like rods and cones, contributing to light-stimulated effects on the body. Müller cells are not part of the visual pathway, but they provide support for the retina and regulation of nutrients and molecules, as well as perform many other functions in the retina.
Winkler, P. (2010). The Nerve Cells of the Retina. The Science Journal of the Lander College of Arts and Sciences, 3(1). Retrieved from https://touroscholar.touro.edu/sjlcas/vol3/iss1/9