The visual system: cell types in the retina. Amacrine cells: functional characteristics of the rod & cone systems. Sensitive to faint light (single photon: due to higher photopigment & convergence. Concentrated in the fovea: most sensitive part of the eye, must constantly move the eye to focus objects of interest on the fovea. Greater acuity (less convergence: flow diagram of the steps in the retina by which light is transduced to action potentials. Sodium channels open, so inward sodium current. Hyperpolarization of rods & cones proportional to amount of light. On = increase in aps; off = decrease in aps. Off surround mediated by inhibitory ( sign-changing ) interneurons around the on centre (see neuro 26: major feature of information processing by the retina. Retinal ganglion cells don"t respond to light per se, but contrast in light shone on the retina. First step of processing in visual system.