Nervous control of walking in the crab, Cardisoma guanhumi

✍ Scribed by Spirito, Carl P. ;Evoy, William H. ;Jonathan, W. ;Barnes, P.

• Publisher: Springer-Verlag
• Year: 1972
• Weight: 737 KB
• Volume: 76
• Category: Article
• ISSN: 0044-362X
• DOI: 10.1007/bf00395497

✦ Synopsis

1. The resistance reflexes evoked by passive movement of the propodactylopodite (P-D) and carl0o-propodite (C-P) joints of the walking legs of the land crab, Cardisoma guanhumi, were analysed quantitatively as a prerequisite to a study of the role of these reflexes in walking.

2. During P-D opening, reflex activity occurs in the slow closer excitor and the peripheral inhibitor to the opener muscle, while during F-D closing firing occurs in the shared opener-stretcher excitor and the stretcher inhibitor (Fig. 1A). Similarly during C-P stretching the motoneurons involved are the slow bender excitor and the stretcher inhibitor and during C-P bending the shared openerstretcher excitor and the opener inhibitor (Fig. 1 B).

3. Reflexes tend to be stronger, both in terms of numbers of spikes and impulse frequency, when the applied movement is towards rather than away from an extreme joint position (Fig. 3).

4. Daring closing and bending movements the responses of excitor and inhibitor are closely coupled. The units have a similar distribution of interspike intervals (Fig. 2) and are strongly phase linked with the inhibitor tending to precede the excitor or be simultaneous with it (Fig. 4B,D). The coupling is less apparent during imposed opening (Fig. 4A) when excitor and inhibitor fire at different frequencies; it is apparently absent during stretching movements (Fig. 4C).

5. Evidence is presented in favour of a model of the reflex system (Fig. 7) in which the observed phase coupling of the motoneurons is the result of a common strong synaptic drive from control units governing each reflex.