Meeting Abstract

62.3  Thursday, Jan. 6  In vitro Control of Muscle Actuators to Understand Animal Movement RAMOS, C.D.; LIM, C.K.; AHN, A.N.*; Harvey Mudd College; Harvey Mudd College; Harvey Mudd College aahn@hmc.edu

Investigating the neural control of a muscle-limb system is essential to understanding how animals move. Although the relationship between stimulation input and force output has been extensively researched, no studies have yet examined how stimulation input (pulse frequency and train duration) affects the movement output of an intact limb with a pair of antagonistic muscles. We hypothesized that the change in joint angle would increase with increasing stimulation duration until a maximum change in joint angle is reached. The plantaris longus (PL) muscle should generate greater joint angle changes than the tibialis anterior (TA) muscle due to its much larger muscle mass. The right leg of Rana catesbeiana (N=26) was surgically removed and attached to a custom-built rig with plastic cable fasteners. The PL and TA were then individually stimulated using a suction electrode on the tibial and common fibular nerves, respectively. Train durations ranging from 5 to 100 ms were tested for frequencies of 5, 25, 50, 75, and 100 Hz. The change in ankle angle, ankle angular velocity, and maximum velocity were then calculated from recorded video at 60 fps. The magnitude of ankle extension for the plantaris muscle was ~50% greater than ankle flexion, much less than the 250% difference in PCSA. Ankle position increased, while angular velocity was independent of stimulation duration at all frequencies. Unexpectedly, the third stimulation pulse generated the maximum angular change regardless of muscle and stimulation frequency. The number of pulses may be a primary determinant of the angular changes about the ankle rather than stimulation pattern. Furthermore, the foot consistently returned to the initial steady state after each disturbance, demonstrating the significance of passive components of the muscle-joint system in determining foot position.