Relation between myofibers and connective tissue during muscle injury repair

The connective tissue framework in skeletal muscle combines the contractile myofibers into a functional unit, in which the contraction of myofibers is transformed into movement via myotendinous junctions (MTJs) at their ends, where myofibers attach to tendons/fascia. The cytoskeletal contractile myo filament apparatus adheres through subsarcolemmal and transmembrane molecul es to the surrounding extracellular matrix, with integrin and dystrophin as sociated chains of molecules being the two main adhesion complexes. In shea ring type of muscle injury both myofibers and the connective tissue framewo rk are ruptured and thereby the functional tendon-muscle-tendon units are d isrupted. The stumps of the ruptured myofibers are separated and at the sam e time joined by a connective tissue scar, through which the ends of regene rating myofibers try to pierce, but as the scar becomes more compact the en ds attach to the scar by new mini-MTJs. During the early phase ruptured myo fibers try to compensate for the lost MTJ attachment by reinforcing their i ntegrin mediated lateral adhesion, which returns to normal low level after formation of the mini-MTJs and at which time complementary increase of dyst rophin and associated molecules on lateral sarcolemma takes place. The stum ps appear to remain separated by and attached to the interposed scar for ma ny months, possibly for ever, i.e. the original tendon-muscle-tendon units may have become permanently divided into two consecutive units. Remarkably, axon sprouts are able to penetrate through the interposed scar to form new neuromuscular junctions on those abjunctional stumps which were denervated by the rupture.