The biophysics of excitability

Summary

To characterize excitability the authors used the method suggested by P. O. Makarov elsewhere. It consists of determining the threshold duration of the stimulus at 3 zones of the strength-duration curve: a) at the utilization time zone, i. e., at the intensity level of 1–3 rheobases, b) at the minimal energy zone (at the level of 2–4 rheobases) and c) at the level of 8–10 rheobases. With the aid of condenser discharges the voltage-duration curves for the motor thresholds of flexors and extensors of the forearm and for the sensory thresholds of the corresponding skin regions were measured. In contradistinction to Lapicque's opinion, the minimum threshold energy is not always in proportion to the chronaxie duration of the stimulus, but corresponds to a rather wide region at the level of 2–5 rheobases. The minimal energy zone of the flexor muscles corresponds to shorter stimuli than that of the extensors. The difference between the sensory and motor thresholds for both flexor and extensor regions is the greater, the shorter the duration of the stimuli applied.