Multifocal innervation and muscle length. A morphological study on the role of myo-myonal junctions, fiber branching and multiple innervation in muscles of different size and shape.
The dependence of the inner organisation and innervation of a skeletal muscle on its size was studied at the level of single muscle fiber architecture and motor endplate topography in muscles of different size, all of them lacking a tendinous scaffolding. The muscles evaluated in this study were: Mm. sternomastoideus, gracilis and latissimus dorsi of the rat and the M. sternocephalicus of the horse. In these muscles a subdivision into two or more 'innervation-compartments' becomes obvious in fascicles reaching a certain length. This provides the possibility of an almost synchronous activation of the entire muscle by its nerve. At the level of single muscle fiber elements, large numbers of myo-myonal junctions were discernible in many sites. However, unequivocal multiple innervation was found, with several end-plates per single muscle fiber, without the interposition of any junctional structure. Myo-myonal junctions, combined with a characteristic branching pattern of many muscle fibers, and scattered innervation sites, obviously play an important role in the architecture of fan-like muscles lacking a tendinous scaffolding.
Zenker
W
W
Institute of Anatomy, University of Zurich, Switzerland.
Snobl
D
D
Boetschi
R
R
D000818:Animals; D006736:Horses; D008297:Male; D009132:Muscles / Q000033:anatomy & histology / Q000294:innervation*; D009210:Myofibrils / Q000502:physiology*; D051381:Rats