Figure 3.

Reflection in a touch cell. Intracellular recordings (lower trace in each pair) were made from the T cell soma in the posterior ganglion. Extracellular recordings (upper traces) from the anterior dorsal root were made differentially between two hooks at the two points marked by dots in Fig. 1A, giving a different appearance to impulses propagating in opposite directions along an axon. The soma was hyperpolarized by current injection to produce reflection. Corresponding impulses in pairs of traces are joined by dotted lines. (A) When the first impulse did not reflect, both impulses followed stimulus artifacts in superimposed traces of the extracellular recording, then arrived at the soma as seen in the intracellular recording. (B) When the impulse reflected, it returned toward the skin (arrow). This impulse collided in the periphery with the second impulse arising in the skin, preventing it from reaching the root electrode or the soma. Impulses arriving from the periphery had a second phase that dropped below baseline (arrowhead). (C) In the root recording, an impulse elicited by intracellular stimulation resembled the reflected impulse in B.