For nerve axon the Hodgkin-Huxley equations, H-H equations or H-H model for short, shows the chaotic response under the periodic electric stimulous. For muscle fiber, Falk and Fatt formulated the Falk-Fatt equations (the F-F equations or F-F model) which are nonlinear equations similar to those of Hodgkin and Huxley. However, the response characteristics of the F-F model has not bee studied in detail. In the present study, several aspects of the H-H model and the F-F model is studied. The H-H model and F-F model are solved with a periodic stimulation (Acosωt, ω=2πf). The chaotic responses are observed under a special condition on an amplitude and frequency. The production procedure of a chaotic response is investigated. In order to investigate the general characteristics of the H-H model and F-F model, an average firing rate is computed and phase variables are drawn in phase plane. Finally, the relationship between the F-F model and the H-H model is considered. For the same periodic stimulation, the F-F model shows the chaotic response and the H-H model shows the n/m phase-locked oscillation or vice versa.