Chronaxie

Chronaxie is the minimum time required for an electric current double the strength of the rheobase to stimulate a muscle or a neuron. Rheobase is the lowest intensity with indefinite pulse duration which just stimulated muscles or nerves. Chronaxie is dependent on the density of voltage-gated sodium channels in the cell, which affect that cell’s excitability. Chronaxie varies across different types of tissue: fast-twitch muscles have a lower chronaxie, slow-twitch muscles have a higher one. Chronaxie is the tissue-excitability parameter thatpermits choice of the optimum stimulus pulse duration for stimulation of any excitable tissue. Chronaxie (c) is the Lapicque descriptor of the stimulus pulse duration for a currentof twice rheobasic (b) strength, which is the threshold currentfor an infinitely long-duration stimulus pulse. Lapicque showedthat these two quantities (c,b) define the strength-duration curvefor current: I = b(1+c/d), where d is the pulse duration.However, there are two other electrical parameters used todescribe a stimulus: energy and charge. The minimum energyoccurs with a pulse duration equal to chronaxie. Minimumcharge (bc) occurs with an infinitely short-duration pulse.Choice of a pulse duration equal to 10c requires a current ofonly 10% above rheobase (b). Choice of a pulse duration of0.1c requires a charge of 10% above the minimum charge (bc). Chronaxie is the minimum time required for an electric current double the strength of the rheobase to stimulate a muscle or a neuron. Rheobase is the lowest intensity with indefinite pulse duration which just stimulated muscles or nerves. Chronaxie is dependent on the density of voltage-gated sodium channels in the cell, which affect that cell’s excitability. Chronaxie varies across different types of tissue: fast-twitch muscles have a lower chronaxie, slow-twitch muscles have a higher one. Chronaxie is the tissue-excitability parameter thatpermits choice of the optimum stimulus pulse duration for stimulation of any excitable tissue. Chronaxie (c) is the Lapicque descriptor of the stimulus pulse duration for a currentof twice rheobasic (b) strength, which is the threshold currentfor an infinitely long-duration stimulus pulse. Lapicque showedthat these two quantities (c,b) define the strength-duration curvefor current: I = b(1+c/d), where d is the pulse duration.However, there are two other electrical parameters used todescribe a stimulus: energy and charge. The minimum energyoccurs with a pulse duration equal to chronaxie. Minimumcharge (bc) occurs with an infinitely short-duration pulse.Choice of a pulse duration equal to 10c requires a current ofonly 10% above rheobase (b). Choice of a pulse duration of0.1c requires a charge of 10% above the minimum charge (bc). The terms chronaxie and rheobase were first coined in Louis Lapicque’s famous paper on Définition expérimentale de l’excitabilité that was published in 1909.