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question may lie with the fact that rod photoreceptors are coupled to one another through
gap junctions.
Figure 4.3 : Current flow in the rod network. The sum of the currents through the membrane
of each rod equals the stimulus current in the source rod.
In the rod network (figure 4.3), signals propagate to adjacent rods through gap junc-
tions in order to cancel random noise in individual cells and increase the number of parallel
channels used in the rod to bipolar cell synapse. [115] One commonly overlooked aspect of
the rod network is that the degree to which signals propagate through the network is de-
pendent not only on the strength of the signal itself and the coupling impedance, but also
on the membrane impedances of the cells in the network. With high membrane impedance
(low conductance), signals tend to dissipate less (figure 4.3, green arrow) and propagate fur-