Actions and interactions of proprioceptors of the locust hind leg coxo-trochanteral joint

Summary

• 1. Reflexes involving hind leg muscles during movement of the coxo-trochanteral joint were recorded after total ipsilateral deafferentation except for one of two groups of mechanoreceptors. These were (i) HP and RH, and (ii) SR1, SR2 and MRO.

• 2. Both groups of receptors influence coxotrochanteral and subcoxal, but not femoro-tibial muscles (Figs. 2, 3; Table 1).

• 3. Many subcoxal muscles are activated by both antagonistic groups of receptors. Their co-contraction may lock the subcoxal joint in a rigid position, thereby making it a firm support for resistance reflexes in more distal joints.

• 4. Reflexes onto coxo-trochanteral muscles were studied in more detail by direct selective mechanical stimulation of single receptors. All receptors elicit typical resistance reflexes: Sense organs sensitive to joint depression (SR1, SR2, MRO) activate levator motor units and inhibit depressor activity (Fig. 4). Sense organs sensitive to levation (HP, RH) cause analogous reactions of opposite sign (Fig. 5).

• 5. Tonic excitation by proprioceptors is necessary to maintain a certain level of spontaneous activity in certain motor neurons. For example after HP and RH extirpation, spontaneous activity of depressor motor units ceases, MRO ablation has comparable effects on levator units (Table 1).