Figure 12. Repetitive firing behaviour of the model motoneuron.

A, with a linearly rising ramp, the model with the standard level of Na_P exhibited good repetitive firing (thin black trace) to a ramp of injected current. The reduced Na_P model failed to generate any spike to this same input (thick black trace). However, adding a series of transient current pulses on top of the ramp, generated spikes in the reduced Na_P model (grey trace), showing it was still capable of initiating spikes to transient inputs. B, behaviour to step inputs: good repetitive firing in the standard model (thin black trace), loss of all but the initial spike in the reduced Na_P model (thick black trace), and failure to restore repetitive firing by increasing the amplitude of the step (grey trace). These simulation results parallel the experimental results for riluzole administration.