FIGURE 1.

Biophysical modelling of spindle Ia afferents. (a) Overview of the methodology used to model Ia muscle spindle firing. Physiological stimuli (ramp–hold–release), recorded during in vivo experiments, were used as inputs (1) to a biophysical model of muscle cross‐bridges to simulate intrafusal fibre dynamics (2). Two components of muscle fibre dynamics were then combined to estimate the muscle spindle Ia receptor potential (conductance) as described in Blum et al. (2020) (3). The receptor potential was the input into the multicompartment biophysical model of the neuronal architecture and ion channel expression and distribution (4) that simulates neural dynamics, for example, spiking (5). (b, c) Three representative cases of spiking activity and corresponding instantaneous firing rates (vertical grey lines and black circles) for Ia neurons recorded in vivo (b) and corresponding model predictions (c). Note the wide biological variability of Ia neurons’ firing profiles and the fact that the model output is well situated within that range. (d) Grey rectangles document the minimum and maximal values of three key encoding parameters recorded in vivo (Housley et al., 2020): average static firing rate (static avg.), peak dynamic firing rate (peak firing) and initial burst. Red circles document model output for same key parameters.