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. Calmodulin activation of troponin is the primary mechanism of initiating the crossbridge cycle. Regulation of crossbridge cycling occurs via activation of the myosin filament as well as the actin filament. There are no sarcomeres and therefore no crossbridges.