Extended Data Fig. 2 |. Motoneuron ion channel dynamics in our biophysical model.

a, Ion currents of a single motoneuron in response to different SCS frequencies (same amplitude, 50%) along with the motoneuron membrane potential during concurrent innervation of residual supraspinal inputs (gray). Ionic currents: L-type Ca2+ (Ical), Ca2+-activated K (Ikca), delayed rectifier K+ (Ikrect), N-type Ca2+ (Ican), and nonlinear fast Na+ (Ina). At low stimulation frequencies (<19 Hz), motoneurons generate action potentials with concurrent supraspinal input for each stimulation pulse. At higher frequencies, motoneurons skip some stimulation pulses due to N-type Ca2+ slow time dynamics. b, Ion currents of the same motoneuron at 45 Hz SCS (50% amplitude) for different conductances of the N-type Ca2+ ion channel. Setting the conductance close to 0 relaxes N-type Ca2+ dynamics constraints. Consequently, less rectifier K+ ions leave the membrane to stabilize the motoneuron membrane potential, leading to a shorter refractory period in the overall motoneuron membrane and producing more action potentials following each stimulation pulse. c, Ion current of the N-type Ca2+ ion channel varying its conductance and its resulting membrane potential. When membrane dynamics allow the entrance of N-type Ca2+ ions, a cascade of Ca2+-activated K ions respond proportionally to counteract this entrance, leading to exaggerated refractory periods in the motoneuron membrane. Arrows indicate stimulation pulses.