Figure 1. f–I relationship for a typical motoneurone.

Cell generates a single spike at a current intensity of 6.5 nA (A), and began firing during the entire 500-ms injection period at an intensity of 7.6 nA (B). Frequencies increase with increasing current intensity (C–E). At a current intensity of 20.7 nA (F), spiking is blocked before the end of the 500-ms current injection period. Minimum current for steady-state firing and minimum steady-state firing frequency (from last three interspike intervals) were measured for this cell from record B, and maximum steady-state firing frequency (from last three interspike intervals) from record E.