What Is the Most Realistic Single-Compartment Model of Spike Initiation?
The compartmentalization hypothesis (B-F adapted from ).
(A) Dual-patch recording of an action potential in soma (black) and in the axonal initial segment (red) (digitized from ). (B) Electrical model of the soma and initiation site (Vs: somatic voltage; Va: axonal voltage; Ra: axial resistance). (C) A current injected close to the soma produces a linear depolarization between soma and injection point (bottom: voltage as a function of distance to soma). The depolarization is proportional to Ra, and therefore to distance (left: injection at 20 μm; left: at 40 μm). (D) Na current (red curve) and axonal current (black lines) as a function of Va when Na channels are placed at 20 μm (left) and 40 μm (right) away from the soma. The 5 lines correspond to Vs between-60 mV and-47.5 mV. (E) Proportion of open Na channels as a function of Vs, with Na channels at the soma (dark blue), at 20 μm (green), and at 40 μm (red) away from the soma. (F) Current-voltage relationship measured at the soma (same color code as in E).