Fig. 4. Effects of repeated brief stretches on the heartbeat rhythm. (A) Example records showing entrainment of the cardiac ganglion (CG) burst rhythm by repeated brief stretches. In each record: upper trace, membrane potential of the heart muscle showing bursts of excitatory junctional potentials (EJPs); lower trace, applied stretch shown by displacement of the unfixed stage. Brief stretches (duration, 300 ms; amplitude, 0.7 mm) were applied at 1.0 Hz (i), 1.3 Hz (ii), 1.7 Hz (iii) and 2.0 Hz (iv). (B) The relationship between the frequency of the CG burst during repeated stretches and the frequency of the stretches. Dotted lines indicate the frequency range of free-running heartbeat (1.44 Hz and 1.61 Hz). A linear regression line in the stimulus range between 1.1 Hz and 1.8 Hz is also shown (y=0.92x+0.11, r²=0.973). Data shown were obtained repeatedly from a single preparation.