Myotendinous connection
Myotendinous connections are specializations of the plasma membrane at the connections of the muscle fibers with the collagen fibers of the origin, attachment and intermediate tendons .
Structure and properties
At the connection points between muscle fiber and tendon, the surface of the fibers is enlarged by numerous tunnel and channel-shaped ("finger-shaped") folds. The increase in area can reach a factor of 10.
On the extracellular side, the basal lamina follows these folds and hugs them. Collagen fibrils are connected to it, which also extend into the depths of the folds. On the intracellular side there are so-called "attachment plaques". These are about 20 nm thick, electron-tight deposits on the plasma membrane into which the actin filaments radiate.
The plasma membrane contains high density receptors (integrins) for the extracellular proteins. Intracellularly, the integrins are connected to the actin filaments of the myofibrils via the proteins talin, vinculin and alpha-actinin.
Frictional connection
This structure ensures the frictional connection of the actin filament through the plasma membrane to the collagen fibrils without exerting high forces on the plasma membrane and destroying its more sensitive structure. This ensures a very direct power transmission of the forces emanating from the actin filaments to the tendons.