Measurement of λeffective was simulated in NEURON as shown in Figure 1A,D and plotted for a representative subspace of the cable model library with a specific membrane resistance (Rm) of 10,000 Ω*cm2, range of specific axial resistances (Ra): 50, 100, 150, and 200 Ω*cm, and a subset of morphologies with proximal diameters (d0) of 0.5, 1, 5, 10, and 20 µm and a constant distal diameter (d1) of 0.5 µm. This cross-section of the cable model library is equivalent to those generating the yellow curves in the leftmost column of plots in Figure 1—figure supplement 1 to Figure 1 (the blue curves in this figure are equivalent to the yellow curves in Figure 1—figure supplement 1 to Figure 1). (A) Array of plots depicting voltage response amplitude (mV) plotted as a function of increasing distance from the site of activation (at 0 µm), illustrating electrotonic decrement of the propagating voltage signal with distance in cables with different Ra values (columns, proximal diameters (d0, rows), and shunt sizes (different colors in key). A large load or unsealed end was achieved by situating a second branch (diameter of 10 µm; Rm and Ra consistent with the parent cable) 300 µm from the proximal end. The size of this shunt was altered by simply changing the length of this appended branch (100, 300, 500, 1000 µm long as in legend). Consistent with Figure 1B and D, while the finer cables yield large distal events that decrement immensely with distance, wider cables yield smaller events that decrement less with distance. It is evident in these plots that unsealed ends with increasing shunt sizes modulate the gain of these curves. (B) Plots showing effective λ as a function of Ra (Ω*cm) for varying shunt sizes (plotted by color as in key). Black horizontal line depicts λeffective = 1 mm, as a reference. Each plot, from top to bottom, corresponds to a different diameter at the proximal end of the cable (d0). The blue shaded region denotes neurite geometries reminiscent of those observed experimentally in secondary neurites of STG neurons (Otopalik et al., 2017a). The gray shaded region indicates neurite geometries that are consistent with those measured in a variety of vertebrate pyramidal neurons. Increasing the shunt size decreases the effective λ across a range of Ra values. However, cables with larger proximal diameters (shaded in blue) and smaller Ra values are somewhat resilient and present λeffective>1 mm for shunts as along as 1 mm.