<prompt> The major cation directly involved in the interaction of actin and myosin in skeletal muscle is:CaNaKMg  <response>: The major cation directly involved in the interaction of actin and myosin in skeletal muscle is calcium Ca. Calcium binds with troponin to cause tropomyosin to uncover the active sites on the actin filaments so that the myosin heads can attach to form cross bridges. Na and K are impoant in the mechanism of the action potential. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. 2012. Chapter 5. Excitable Tissue: Muscle. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks Eds,Ganongs Review of Medical Physiology, 24e. 