Fig. 5. Electrical and mechanical responses of the SBM. (A) Superimposed recordings of a single isometric twitch in response to a single motor nerve stimulation and a series of twitches in response to repetitive motor nerve stimulation at 100 Hz. The upper and lower traces show action potentials and twitches, respectively. (B) Steady isometric tension in response to transverse a.c. field stimulation (100 Hz).