Fig. 10.

Spikes can be initiated in the lateral process during motor programs. A motor program was induced by stimulation of CBI-2. In this preparation, an unusual amount of centrally induced activity was observed in B21. Only the retraction phase of the motor program is shown in its entirety. Left, Current was not injected into B21. Note that spikes are recorded from both the soma and lateral process. Right, To determine whether spikes originated in the soma or lateral process, hyperpolarizing current was injected into the soma. Many spikes were attenuated in the soma but remained full-size in the lateral process, suggesting that they were initiated in the lateral process. Inset, High-speed recording of the region indicated by the arrow.b, Note that, when spikes were full-size in the lateral process and attenuated in the soma, the peak of depolarization in the lateral process preceded the peak of depolarization in the soma.a, Note that the soma also appeared to be receiving synaptic input, and some depolarizing potentials were larger and peaked earlier than corresponding potentials in the lateral process.L, Lateral; S, soma.