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Fatima Pedrosa Domellof, Linda K McLoon, Mona Lindström; A sturdy connective tissue network surrounds all the extraocular muscle fibers. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
Recent reports suggest that the different compartmentss of the extraocular muscles can contract independently. As this is in contrast to how other skeletal muscles function, we examined the connective tissue endo-, peri-, and epimysium to determine the biological feasibility of this view.
Normal human EOMs were serially cross-sectioned and processed for immunohistochemistry with antibodies specific against Collagen I, III IV , VI and elastin. Human and rabbit EOMs were fixed and processed for scanning electron microscopy (SEM).
Col III, IV, and VI nicely delineated the contours of all muscle fibers, and Col VI was also found in the perimysial space. In contrast, Col I was mostly present in the interstitial perimysial space. Elastin was found surrounding individual myofibers both circumferentially and longitudinally, as well as running between neighboring fibers. Col I, VI, and elastin were all seen to run equally between all parts of the muscle, including between the orbital and global layers.SEM revealed a very prominent network of fibrils around the individual muscle fibers, showing a network of highly interconnected and sturdy channels within which the fibers are contained. These interconnected networks ran from the epimyisum to the endomysium around each myofiber, forming a continuous and prominent network, with a continuous and tight matrix interconnection between the orbital and global layers.
This massively interconnected collagen matrix likely results in significant lateral force transmission. This finding helps explain the ”loss of additive force” seen in experiments where the stimulation of multiple motor units does not equal the sum of the forces of each stimulated singly. It also supports the view that individual compartmental movements could not be possible if the epimysium is intact.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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