Feeding Motor Patterns in Anurans: Insights from Biomechanical Modeling

During feeding in anurans, the mouth opens while the tongue, which is attached to the mandible at the front of the mouth, rotates forward. Due to the relative simplicity of its anatomy and the complexity of its motion, tongue protraction in frogs presents an ideal system for exploring the neural control of multijoint movements. In this study, we used a forward dynamic, rigid body model with four segments and two muscles to investigate open loop control of tongue protraction in the Australian white-lipped tree frog, Litoria caerulea. Model parameters include the mass distribution, initial position and initial angular velocity of each segment and the anatomy and physiology of each muscle. Model variables include the level of muscle activation at each time step and impulsive torques to open and close the mouth. The model gives X,Y coordinates of each segment and joint angles at each time step as output. The model was tested using scaled, normalized EMG signals and impulsive joint torques to predict the paths of the lower jaw tip and tongue tip. Predicted paths were compared to experimentally observed paths using Pearson product-moment correlation coefficients. Simulations demonstrate that the genioglossus muscles likely play a minor role, if any, in determining the trajectory of the tongue in most anurans. Most of the force for tongue protraction comes from angular momentum transferred to the tongue by the opening jaws. In anurans, tongue protraction is dynamically stable and will occur as long as the musculoskeletal elements are in the correct initial position.