Fig. 9. Sequential experiment in which a single electrode was placed in a circular muscle cell (at the site marked R in the diagram), and a stimulating suction electrode was moved to the sites marked A, B and C. For trace A, the stimulus was delivered in the same segment as the recording site (stimulus site A), and a junctional potential was triggered with a short latency. Three spontaneous action potentials were also recorded, and each was initiated by a junctional potential of similar size to those electrically stimulated (note the slight inflection on the rising phase of the action potentials). When the stimulating electrode was moved over one segment (stimulus site B and trace B), junctional potentials were triggered by three of the four stimuli, but with a longer latency than in trace A. Following the second and fourth stimuli, weak contractions were initiated. The electrode was then moved over one more segment (stimulus site C and trace C). Electrical stimuli sufficient to produce weak contractions in the stimulated segment did not initiate junctional potentials in the recorded segment (two segments over). A few junctional potentials were recorded during these experiments (one is shown in this trace), however, they showed no regular relationship to imposed stimuli. It appears these are spontaneous events. Delivery of stimuli is marked by the stimulus artifacts (arrows). The recording site was 2.5 mm from the top of the nerve ring.