The name is absent

98

5.5 Estimation of adjacent coupling resistance

The measurements made using voltage clamp in section 5.3 measure the apparent resistance
R_a between two cells through the entire network, not the resistance R_c that connects the two
adjacent cells. When the length constant is short, these values are comparable. The network
resistance between two cells is an interesting parameter because it can be measured directly
from the retina, and estimates the degree of coupling between cells. It also serves as a lower
bound on the possible value for R_c. However, by itself, R_a is useless to create a model because
many combinations of 7 = R_c∣ R_m could produce a recorded network conductance. Here,
we show that for a given input input impedance and length constant, there is one network
resistance for adjacent cells.

Input impedances may vary from cell to cell, so to obtain an estimate of R_c from R_a,
the input impedance of the particular cell being recorded is important. While the input
impedance of each cell was not recorded during the voltage clamp experiments, it can be
estimated by making two assumptions. If we assume (1) that the input impedances of the
pair of cells being recorded are equivalent, and (2) that the holding potential of the follower
cell (-40 mV) is near the resting potential for rods, then we can solve for the input impedance
of each cell Ri_n2D∙

The voltage distribution can be described by a system of two equations from the su-
perposition of two point sources of current in the network, as shown by figure 5.5. These
equations are as follows, where K is the voltage decay from the source to the neighboring
cell. Vq is the voltage (and ⅛ the current) in the driver cell, and v₁ is the voltage (and ⅛ the

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