Figure 1. Dynamic interactions between I _Na and V _e in a disc‐shaped membrane (R _disc = 11 μm) separated from a non‐conducting obstacle by an extracellular cleft (uniform distribution of g _Na, F_{g Na} = 10.09).

A, schematic representation of the model (left: cross‐section; middle: finite element mesh) with membrane capacitance, ion currents and extracellular resistive properties (blue). V _e at the rim of the disc was held at 0 (red). Due to radial symmetry (uniform Na⁺ channel distribution), the model behaviour does not depend on the azimuthal coordinate but only on the radial coordinate (right). B, left: total I _Na during an activation step from −85 mV to −25 mV (top) and to −50 mV (bottom), for various cleft widths. B, middle: corresponding colour maps of V _e, I _Na, m ³ and hj as a function of time and distance from the centre, for a 20‐nm‐wide cleft. C, spatial profile of V _e at the occurrence of the minimum (arrow in the middle panel of A) for V _step = −25 mV and a cleft width of 20 nm. D, minimal V _e registered in the cleft as a function of cleft width, for V _step = −25 mV and −50 mV. Note the abrupt behaviour for V _step = −50 mV (blue arrow). E, relationship between peak total I _Na and V _step for various cleft widths (left) and derived steady‐state activation curves (right).