Fig. 6.

In situ extracellular recordings from tethered swimming leeches. Nerve impulses recorded from the DP nerves were generated by motoneurons DE-3, which command dorsal longitudinal muscle contraction during swimming. DE-3 neurons generate one burst of impulses per swim cycle; relative timing of DE-3 bursting in different segments was used to measure intersegmental phase relationship. A, An intact preparation (left) and an SNC preparation (right; different animal). B, A sample record from the intact leech. DE-3 activity in M7 and M14 was phase-locked, with a phase lag of less than one-third of a cycle. C, A sample record from the SNC leech. DE-3 activity in M7 and M14 was again phase-locked after nerve cord transection, but the phase lag between them is now approximately one-half of a swim cycle. [DP(7), DP nerve from M7; DP(14), DP nerve from M14. In theDP(14) trace in B and bothtraces in C, the largest spikes were identified as T-cell impulses by their large size and their activation by light touch.]