Structure determines function of the retina, a neural center. 2. The second, third and fourth circuits.

Three retinal circuits are analyzed on the bases of established circuit diagrams. The synaptic interaction at one circuit involves depolarizing bipolar cells connected to rods and shows the important contribution to function of the connections between cones and rods including connections of cones to bipolar cells connected to rods. Another circuit explains that one type of bipolar cell is depolarized at cessation of the stimulus. Because each photoreceptor is connected to both on- and off- bipolar cells, on- and off- responses are generated from each photoreceptor. The cone connections to rods and to bipolar cells connected to rods extend rod vision to low ambient illumination while the absence of corresponding connections at cone terminals leads to cone vision being blocked at low ambient illumination. The cone connections raise the threshold for stimulation of bipolar cells connected to rods and lower temporal resolution of rod vision relative to cone vision. The timing of interaction between bipolar cells, amacrine cells and ganglion cells in the inner plexiform layer makes inhibitory and facilitatory modulation of ganglion cell potential establish optimal conditions for ganglion cell activation. The agreement between bipolar cell responses determined on the basis of the analysis of the circuit diagrams and the responses recorded from bipolar cells shows that the function of a neural center such as the retina can be analyzed on the basis of circuit diagrams.