English to Portuguese Science Mathematics & Statistics Dynamical Systems

Figure 13-K displays the direction and magnitude of transmembrane currents (1m) along the fiber at the instant (to) at which excitation has reached site Xo. Current flow is inwardly directed in fiber regions that have just undergone activation (i.e., to the left of point Xo) and outwardly directed in neighboring zones still at rest (i.e., to the right of Xo). Sites of outward current flow are current sources and those with inward current flow are current sinks. As depicted in the figure, current flow is most intense in each direction near the site of activation, Xo.
Because the border between inwardly and outwardly directed currents is relatively sharp, these currents may be visualized as if they were limited to the sites of maximal current flow, as depicted in Figure 13-1 D, and separated by a distance, d, that is usually 1.0 mm or less. As activation proceeds along the fiber, the source-sink pair moves to the right at the speed of propagation in the fiber.