Figure 2. Spontaneous and evoked contractions recorded simultaneously in both muscle layers in intact segments of intestine.

A, ongoing activity in both the circular (CM, balloon pressure change, mmHg) and longitudinal (LM, transducer output in volts) muscle layers. The circular muscle remained quiescent for long periods, whereas a slowly changing baseline activity was seen in the longitudinal muscle. Occasional larger and faster contractions occurred at random intervals (asterisk), and most often involved both muscle layers. B, contraction seen at the asterisk in A on an expanded time scale. C, contraction evoked in both muscle layers by transmural electrical stimulation (onset at arrow, 1 ms, 100 V, 5 Hz, 1 s train) applied at the anal end of a different segment of intestine. Note differences in the configurations of responses in circular and longitudinal recordings. Pressure and voltage scale bars in C apply to all panels. Time scale in C applies to panels B and C.