A Model of Force Generation by Locust Skeletal Muscle in Response to Individual Stimuli

Abstract

A mathematical model of the locust hind leg extensor muscle is presented. The model accounts for the force response of the muscle due to individual stimuli under isometric conditions. Experimental data was collected by stimulating the muscle directly and force measured at the tibia. Joint dimensions were calculated, enabling tibial force to be converted into muscle force. In developing a model it was assumed that the response to a single isolated stimulus was linear, but no assumptions were made about the model order. Models of various order were fitted using time and frequency domain methods to data obtained from well-separated input pulses. The response could be approximated as an impulse response, with the response to each stimulus best described by a linear third-order system. Responses where input pulses were not well-separated, so that summation of subsequent pulses occurred, were also investigated. As has been observed in mammalian muscle, both facilitation and force depression were evident in locust muscle. The linear third-order model was found to provide an adequate fit to data in which depression and facilitation were evident if the parameters describing the system were allowed to vary between each response.