Figure 2.

Quantification of the determination of θ in a computer model. The cable equation identifies r_a, c_m, and i_i as the determinants of θ, but does not clearly demonstrate the magnitudes of their influences. Computer modeling of a skeletal muscle fiber (Fraser et al., 2011) shows the influence of r_a (panel A), c_m (panel B), and i_Na(max) (panel C) on AP waveform (i), dV/dt (ii), and θ (iii). In panels i and ii, three representative APs are shown, each stimulated at 1s and recorded 2.5 mm further along the cable, such that increased times to the AP peaks denote slowed conduction. In panel iii, the velocities of these APs are labeled 1, 2, and 3. It will be noted that r_a influences θ but not AP waveform, whereas c_m and i_Na(max) each influence AP waveform and θ. Note that in panel C(iii), θ is plotted against both i_Na(max) (upper scale, squares) and P_Na(max) (lower scale, triangles). The simple quantitative relationships between these parameters that emerge from this analysis are given in the text.