Mandibular movements and their conrol inHomarus gammarus

1.Electromyograms were recorded from the major muscles responsible for the mandibular opening and closing movements in the lobsterHomarus gammarus. Concomitant mandibular movements were also monitored.2.Animals were fed a standard substrate (Nephrops leg) to obtain standard responses. They were then fed an incompressible substrate (metal tube) and an elastic substrate (rubber rod) for comparisons of feeding behaviour, mandibular movement and muscle activity.3.In comparison with the standard substrate the incompressible substrate caused an increase in bite frequency (Fig. 2 A, B) with closer muscle activity occupying a reduced fraction of the cycle. The overall changes in cycle structure could not be explained in terms of the shorter cycle alone (Fig. 4 A, B). There was a marked and sudden increase in closer muscle activity when the mandibles engaged the incompressible substrate (Fig. 2C). The intra-cycle relationships became very strong with significantly less variation around values (Fig. 5A, B).4.In comparison with the standard substrate the elastic substrate caused the animal to reduce its rate of biting with sustained closer muscle activity occupying almost all the prolonged cycle (Fig. 6 A, B). The overall changes in cycle structure could not be explained in terms of the longer cycle alone (Fig. 8 A, B). The increase in closer muscle activity upon engagement of the substrate was not markedly different from the standard case but the termination of the closer activity was altered so that the level of activity fluctuated widely before tailing off (Fig. 6C). The intra-cycle relationships became weaker with more variation around modal values (Fig. 9 A, B).5.The results were considered in context with related findings and a mechanism hypothesised in which a basic centrally generated biting pattern is considerably modified by both position (proprioceptive) and tension (load) sensitive afference from the mandibles.