A myocybernetic model of the jaw system of the rat.

A dynamic model of the jaw system of the rat has been formulated. The model consists of several units: (1) A static muscle fiber model, relating force with fiber length, based on sarcomere morphometric information. (2) A static skeletal muscle model, relating muscle force with muscle length based on myomorphometric information and the static fiber model. (3) A dynamic skeletal muscle model, relating muscle force with muscle length, contraction velocity and stimulation rate, based on fiber type data, calcium dynamics and velocity-force relations and on the static skeletal muscle model. (4) A kinematic model of the jaw system, relating the possible movements of the jaw system with the morphometrics of the bones, joints and connective tissue. (5) A three-dimensional reconstruction package, devised to analyze and display the morphometrics of the jaw system and to show the model results in terms of force vectors, positions and movements of the jaw system. EMG data of chewing rats and myomorphometric data (from unit 5) are fed into unit 3 resulting in muscle forces. The trajectories of the lower jaw and hyoid resulting from these velocity-dependent forces are calculated using unit 4, taking inertias and gravity into account. The calculated movements are remarkably similar to those that have been observed experimentally. The force-velocity relation of the muscles is highly important in stabilizing the velocities of the elements.