THE CUTICULAR STRESS DETECTOR (CSD2) OF THE CRAYFISH II. ACTIVITY DURING WALKING AND INFLUENCES ON LEG COORDINATION

SUMMARY 1. When a crayfish walks forward, its legs are not loaded equally. The third pair is the one exerting the largest vertically directed force, and the fourth legs produce the major part of the propulsive force. 2. Chronic recordings from a CSD2 nerve were made in crayfish walking on a treadmill. The activity of CSD2 rises during the stance phase. The activity peak at the beginning of the power stroke is especially pronounced in leg 4, which was studied in detail. The average spike frequency of CSD2 recordings during the first part of the power stroke is positively correlated with the initial increase in force produced by the leg. This suggests that CSD2 responds especially well to rapid load changes. 3. When a wire was fixed around a fourth leg such that it depressed the patch of compliant cuticle associated with CSD2, the activity of the sense organ was elevated throughout the entire step cycle, and the time between leg 4 touching the ground and leg 3 lifting off was more variable than in normal walking. Thus, CSD2 seems to be involved in the coordination of the walking legs. 4. Depressing the compliant cuticle of CSD2 elicits reflexes in the flexor muscle and the anterior levator in tethered crayfish. Interleg reflexes were not found.