The A . In all three muscle types, skeletal, cardiac and smooth, activation of contraction involves a rise in sarcoplasmic calcium concentration. In all three muscle types the effect of calcium on the crossbridge cycle is via calcium activation of a regulatory protein. In all three muscle types, activation of contraction is primarily by way of alterations on the actin filament. In all three muscle types, activation of contraction results in an increased myosin ATPase activity.
Muscle fibers have only one type of neural activation, which causes a positive response.
Action potentials are of relatively long duration compared to neuronal action potentials. The sliding of actin against myosin filaments results from actomyosin ATPase activity. Individual sarcomeres are visible by light microscopy. Gap junctions act as mechanical links, holding muscles together as they contract. Activation of several motor units simultaneously is one mechanism of controlling contractile strength.