The role of the submentalis muscle in neuromechanical control of tongue movements in Bufo marinus

Abstract

Our lab is studying the feeding behavior in the marine toad, Bufo marinus, as a model system for the neuronal regulation of coordinated movement. Previous studies have suggested that the brainstem coordinates precise movements through a muscular 'trigger' that signals and initiates pre‐loaded muscle activation. We investigated a small distal muscle in the lower jaw, the submentalis, as the trigger for the feeding behavior in toads. The innervation of this muscle was identified, as well as the distribution of trigeminal nuclei innervating the submentalis. Using high speed videography, we analyzed jaw‐tongue movements before and after denervation of the submentalis. Following denervation, the toads were unable to completely protract their tongues. However, tongue protraction gradually increased and full tongue protraction and successful feeding behavior was observed after 4‐6 attempts, suggesting a potential model for motor learning. Additionally, we have anatomically identified the presence of muscle spindles in the submentalis, suggesting that proprioceptive afferents are regulating the motor output. These data support the idea of the submentalis muscle acting as a trigger for timed feeding movements and the importance of the submentalis in coordinating jaw‐tongue movement.