Electric current flow inside perineurial sheaths of mouse motor nerves

Micro-electrodes were inserted inside the perineurial space to record external currents along the superficial nerve bundles of the triangularis sterni muscle of the mouse upon motor nerve stimulation. Two kinds of external currents were distinguished, the first circulating between neighbouring nodes of Ranvier in each fibre and the second circulating between the nodes and the motor endings. Ending-node current was caused by differences in the time course and the amplitude of the potential change at the endings and at the nodes, which depended in turn, on differences between their respective membrane conductances. The stretch of nerve over which ending-node current extended served to estimate that about eight to ten nodes of Ranvier supply the motor endings with depolarizing current.