Reflex antennal movements in the spiny lobster,Palinurus elephas

Summary

• 1. The antennal responses of the spiny lobster,Palinums elephas, to tilting movements of a platform held under the animal's legs and to passive movements of the antenna were analysed in order to study why resistance reflexes were readily produced by passive (imposed) movement but did not occur during active (reflexive) movement (Fig. 2A, B).

• 2. Since antennal movements imposed during platform tilts induced resistance reflexes (Fig. 2C, D), resistance reflexes were not inhibited during active movements, nor did they give way to assistance reflexes.

• 3. Imposed antennal movements that exactly duplicated the immediately preceding antennal responses to platform oscillation induced resistance reflexes, showing that the active antennal movements were within the range of amplitudes and velocities that generated such reflexes (Fig. 3).

• 4. The effects of immobilizing the antenna on the antennal responses to platform tilts were somewhat variable when the antenna was fixed at or near its mid-position (Table 1). In contrast, fixing the joint near either of its extreme positions induced a position effect whereby the responses of the muscle that moved the antenna away from the extreme position were augmented, those of the muscle that moved the joint towards the extreme position decreased.

• 5. Placement of a block in the path of a moving antenna during platform tilts usually led to a positive feedback reflex in that activity in the muscle that encountered resistance to contraction was augmented (Figs. 5, 6, 7B).

• 6. In two preliminary experiments the effects of ablation of the chordotonal organ spanning the J1 joint on the above responses were examined. Resistance reflexes were abolished by the operation (Fig. 7C, F) as were the blocking effects (Figs. 7B, E, 8); antennal responses to platform tilts were largely unaffected (Figs. 7A, D, 8A, C).

• 7. Although the data were not a perfect fit to a model of motor control incorporating both negative feedback and efference copy elements (Fig. 1), the motor control system governing antennal movement has many of the properties of a von Holst type reafference system. It is proposed that corollary discharge interneurons, driven by the central commands for movement, prevent active movements initiating resistance reflexes (Fig. 9).