We have structured a simulation of an antidromic impulse, by using a realistic cell model, compartmentalized and visually expanded using the Neuron simulator. In the simulation shown in the animation below, an antidromic impulse was started in the distal axon and propagated into the soma. The model used for this simulation is the five-channel model developed by Fohlmeister and Miller (Fohlmeister and Miller, 1997a & b) and the channel densities are illustrated in this table. The anatomical constraints include multiple, tapering sections from the NR to the distal axon and the proximal AH. As the impulse propagates through the NR and approaches the AH, it begins to fail, even though the Na⁺ channel density in the NR is relatively high. Nevertheless, at these channel densities, an impulse in the AH and soma-dendritic tree takes place. This result accurately simulates the physiological studies based on whole-cell recordings. In order for the NR to conduct nerve impulses the Na⁺ channel density must be relatively high and, for the orthograde impulse to function properly, the soma and the dendritic tree must contain Na⁺ channels. Although the actual site of impulse initiation in retinal ganglion cells has not been identified, the presence of elevated Na⁺ channels in the AH and NR suggests that both structures play an important role in the early stages of impulse generation and propagation towards the brain.

The top panel shows a plot of part of the reconstructed cell morphology. Membrane voltage is indicated by the color scale shown on the left. The bottom left panel plots membrane voltage as a function of simultation time. Different color traces are the voltages occuring in different locations within the cell. The bottom right panel plots membrane voltage as a function of distance from the soma (at a value of approximately -200 microns) and out along the length of the axon. The antidromic spike will appear on the right of this space plot and propagate toward the soma (to the left in the graph).