Firing threshold curves. (Top) Threshold current for action potential firing as a function of frequency for various values of model parameters. The nominal case was a cable with a radius of 7 μm, gap junctional resistances (RGJ) of 10 MΩ, and intracellular conductivity (σi) of 10 mS/cm. (Bottom) Effect of sodium channel manipulation on current threshold. The threshold to fire is plotted for conditions under which the m gate kinetics were decreased by 10 (τm × 10), the h gate kinetics were increased by 10 (τh/10), the j gate kinetics were increased by a factor of 10 (τj × 10), and a passive cable was used. See text for details.