NISHIKAWA, KC*; LAPPIN, AK; MONROY, JA; PILARSKI, JQ; PIEROTTI, DJ; Northern Arizona University: Neuromechanics of elastic energy storage and recovery during ballistic movements

The goal of our research is to understand the biomechanics and neural control of ballistic movements, using tongue projection in frogs as a model system. Ballistic tongue projection is an extremely rapid, goal�directed movement that requires the coordinated action of numerous muscles. We developed a forward-dynamic, multi-joint model to investigate mechanisms of inter-joint coordination. The model demonstrates that ballistic tongue projection is dynamically stable. Thus, active CNS control is constrained by the mechanics of the feeding apparatus. More than 90% of the force for tongue projection comes from the depressor mandibulae muscles via transfer of momentum from the lower jaw to the tongue. We used in situ force-lever experiments and an elastic recoil model of the depressor mandibulae muscles to investigate the roles of storage and recovery of elastic strain energy in powering ballistic tongue projection. The depressor mandibulae muscles are activated for up to 250 ms prior to movement. The force produced by the depressor mandibulae muscles prior to movement determines not only the displacement of extra-muscular connective tissues and the muscles themselves, but also the total stiffness of the jaw apparatus. In principle, the CNS could control ballistic tongue projection simply by specifying the force in the jaw depressors prior to movement and the timing of rapid unloading. The resulting movement of the lower jaw and tongue is determined by the load-dependent elastic properties of the feeding apparatus. Proprioceptive afferents control the recovery of elastic strain energy by modulating the activity of levator mandibulae muscles prior to mouth opening. Supported by NIH R25-GM56931 and NSF IBN-0240349.