One mechanical property of contraction of isolated bullfrog geniohyoid muscle

: In general, skeletal muscle activity has been understood on the basis that the muscle is functionally consisted of contractile element and elastic element. In this paper it has been attempted to clarify the specific role of the geniohyoid muscle which is one member of the oro-basal muscular system, because our previous reports suggested an elastic specificity of only this muscle as supposed, for example, from the presence of posttetanic twitch attenuation under isotonic condition. For this reason, the experiments have been carried out with paying attention to an interrelationship between loading and contraction figure. When the geniohyoid muscle, weighing over 320 mg, was contracted without any loading, downward undulation under the base line (abbreviated by negative deflection) could be obviously seen within the period succeeding after a falling or relaxation phase of a contraction curve. This negative deflection which presumably indicates the elastic behavior disappeared with increasing the loads from nothing to 4 times the muscle weight. This 3-4 times loading was peculiar to the geniohyoid muscle. In the same situation, 4-5 times loading was specific to the rectus abdominis muscle, and 7-8 times loading was specific to the sartorius muscle. Furthermore, when the geniohyoid muscle was divided first to 1/2 and then to 1/4, the negative deflection of each muscle block was shifted to the lighter side of the applied load. Additional experimental results will be accumulated in the next report.