The way a neuron undergoes rest-spiking transitionsdetermines the type of excitability and the computationalproperties of a neuron. Such transitions are particularlyimportant in the motor system, specifically with respect tomotor-unit recruitment and gradation of force. If weregard the electrophysiological activity of a neuron as adynamical system, the rest-spiking transition can bethought of as a bifurcation. That is, a qualitative change inthe trajectories followed by the variables in the system.Recordings from Drosophila neurons show that the spik-ing activity of a neuron undergoes qualitative changes asoccurs after genetic manipulations that affect the popula-tion of potassium channels [1]. We developed a singlecompartment model of the dynamics of the identifiedmotor neuron MN5 from Drosophila based on publishedexperimental results [2]. In vivo, MN5 controls the dorsal-longitudinal fiight muscle, firing trains of action poten-tials with a frequency between 6 and 25 Hz depending onthe excitatory drive it receives. Bifurcation studies wereperformed to elucidate the changes in phase space as afunction of different biophysical parameters includinghalf activation potentials, gating charge, close-open ratesand number of membrane channels. Bifurcation analysisand simulations predict that the number of channels andthe half-activation potential for the delayed rectifiers andA-type potassium channels can explain changes in spikingbehavior resulting from genetic manipulations asreported in [1,2]. For instance, decreasing the half activa-tion potential for the delayed rectifier channel induces achange in bifurcation from saddle-node (no subthresholdoscillations before spiking) to Hopf (subthreshold oscilla-tions before sustained spikes). Biophysical parametersobtained from MN5 patch clamp recordings will be usedin the future to restrict the parameter space specifically forMN5. The theoretical results from this study can be testedusing targeted genetic manipulations of potassium chan-nels.