Modeling of sarcomere and muscle

Modeling of myosin arm

Property of myosin arm spring

In XB Modeler, we assume that myosin arm behaves like a linear spring for positive stretches while a nonlinear behavior is introduced for negative stretches based on the slacks of myosin arm [Kaya et al., 2010] as depicted in the stretch (x)-force (F_arm) curve (black) below. The strain energy W_arm is given by integrating the force F_arm from x=0. In XB Modeler, the sum of all forces generated by the myosin arms gives the contractile force of muscle. You can adjust the spring constant k_xb of the myosin arm by clicking Edit Parameter in the menu bar of your model editor page and then clicking the Spring tab.

[Kaya et al., 2010] M. Kaya and H. Higuchi. Non-linear elasticity and an 8 nm working stroke of single myosin molecules in myofilaments. Science 329, 686-689 (2010)

Determination of initial arm stretch

XB Modeler determines the initial arm stretch x_init at the transition form a no binding state to a bind state from the Boltzmann distribution given by the strain energy W_arm. XB Modeler holds the inverse function of Rand(x) and applys it to a given random number between 0 and 1 to determine x_init, when a transition from a no binding state to a binding state takes place.