NISHIKAWA, K.C.: Feeding motor patterns: Insights from biomechanical modeling.

Biomechanical modeling and empirical studies in my laboratory over the past ten years have produced a number of insights into activation patterns of tongue and jaw muscles during feeding in frogs. One insight from empirical work, confirmed by biomechanical modeling, is that activation patterns of antagonistic muscles change with body size. For example, in toads, the onset time of the tongue retractor muscles relative to the tongue protractors changes systematically with body size. This occurs because the contraction and relaxation times of individual muscles are independent of body size, whereas the duration of activation is directly proportional to linear dimensions. As animals grow, the relative onset times of muscles change so that peak force is developed at the same time during the feeding cycle. The implication of such considerations is that neither are muscle activation patterns constant during the lifetime of individuals within a species, nor can they be characteristic of a species as a whole. A second insight from biomechanical modeling, which is consistent with a large body of empirical work, is that the genioglossus muscles of frogs, long considered as tongue protractors, are actually an order of magnitude too small to affect the tongue trajectory during protraction. Tongue protraction is dynamically stable, and is powered mostly by angular momentum transferred from the opening jaws to the tongue. Connective tissues in the tongue are designed to resist or permit tongue elongation. We hypothesize that the genioglossus muscles themselves, rather than powering tongue protraction, may perform some other essential role, such as breaking surface tension between the tongue and the lower jaw. Biomechanical models, coupled with empirical studies, often suggest functional hypotheses that are not intuitively obvious.