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Scanning electron microscopy of the endomysial collagen in the rat paravertebral musculature
=========MNALS Of ANATOMY = = = = = = = = = Short communication Scanning electron microscopy of the endomysial collagen in the rat paravertebral musculature V. Vasilev, D. Andreev and W. Kiihnel* Department of Anatomy, Histology and Embryology, Academy of Medicine, G. Sofiiski1, BG-1431 Sofia, Bulgaria, and * Institut fur Anatomie, Medizinische Universitat zu LUbeck, Ratzeburger Allee 160, D-23538 LUbeck, Germany
As has been shown by previous investigations, the connective-tissue components of a striated muscle (the endo-, periand epimysium) consist mainly of collagen fibers, a fact which has an essential bearing on the shape, mechanics and viscoelastic properties of the muscle (Borg et al. 1982). However, the existing literature data on the organization of these structures is scanty and somewhat conflicting (Borg and Caulfield 1980; Rowe 1981). It is the purpose of the present work to study the spatial organization of the endomysial collagen, since the endomysium represents the most important part of the connective-tissue framework of a muscle. The scanning electron microscope is the ideal instrument for this investigation. Material from the paravertebral musculature of adult Wistar rats was routinely processed for scanning electron microscopy. We used a Phillips SEM 505. Three types of collagenous structure were observed surrounding and lying between the muscle fibers . Those of type one consist of a dense network of undulating collagen fibers lying on the surface of the muscle fibers (Fig. 1). The type two structures are made up of bundles of collagen fibers lying transversely between the muscle fibers, and binding them either to one another (Fig. 2), or to the neighbouring blood vessels. In a substantial number of these, globular elements are to be found, whereas in others, elastin-like material has been observed. The ends of the collagen fibers in these bundles become separated into branches, which diverge and become entwined with the sarcolemmic reticulum on the surface of the muscle fibers (Fig. 3). Apart from the collagen bundles between the myofibers, single
Correspondence to: V. Vasilev
)!I£ SEMPER
Ann Anat (1995) 177: 85 - 87 Gustav Fischer Verlag Jena
collagen fibers running in various directions and binding contiguous myofibers to each other and to nearby blood vessels were also seen. These fibers were assigned to the third type of endomysial collagen structure (Fig. 3). In some places they are closely bound to each other by their own branches, thus building up a loose reticulum. Their attachment to the muscle fibers is similar to that of the collagen fibers in the bundles.
Fig. 1. Sarcolemmic reticulum (SR) of collagen fibers on the surface of a muscle fiber (M). x4610
Fig. 2. Collagen bundles (B) connecting two contiguous muscle fibers (M). Within these bundles globular bodies of variable size can be seen (arrows). x2270
Fig. 3. Collagen bundles (B) and single collagen fibers (F) binding muscle fibers (M) to one another and to an adjacent capillary (C). x1500
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The results obtained point to a three-dimensional endomysial collagen architecture, comprising three types of interrelated structure. The sarcolemmic reticulums covering individual myofibers play an essential role in this formation. Because of the mechanical resistance of collagen, they distribute the tensile forces during contraction and passive stretching of a muscle evenly, and thus prevent overstretching of the muscle fibre. On the other hand, owing to the undulating configuration of the constituent collagen fibers, these structures may also function as elastic system, promoting the relaxation of the muscle cell and assuming the role of shock-absorber in the event of a sudden contraction or strain. The other two types of endomysial collagen structure, i. e. the collagen bundles and the individual collagen fibers, bind the sarcolemmic networks of adjacent myofibers to one another or to the vascular walls. In this
fashion they contribute to the structural and functional integration of the individual muscle fibers as well as to the maintenance of an optimal blood flow through the muscles themselves.
References Borg T, Caulfield J (1980) Morphology of connective tissue in skeletal muscle. Tissue and Cell 12: 197- 207 Borg T, Sullivan T, Ivy J (1982) Functional arrangement of connective tissue in striated muscle with emphasis on cardiac muscle. Scanning Electron Microsc 4: 1775 -1784 Rowe R (1981) Morphology of perymysial and endomysial connective tissue in skeletal muscle. Tissue and Cell 13: 681 - 690 Accepted September 18, 1993
87
As has been shown by previous investigations, the connective-tissue components of a striated muscle (the endo-, periand epimysium) consist mainly of collagen fibers, a fact which has an essential bearing on the shape, mechanics and viscoelastic properties of the muscle (Borg et al. 1982). However, the existing literature data on the organization of these structures is scanty and somewhat conflicting (Borg and Caulfield 1980; Rowe 1981). It is the purpose of the present work to study the spatial organization of the endomysial collagen, since the endomysium represents the most important part of the connective-tissue framework of a muscle. The scanning electron microscope is the ideal instrument for this investigation. Material from the paravertebral musculature of adult Wistar rats was routinely processed for scanning electron microscopy. We used a Phillips SEM 505. Three types of collagenous structure were observed surrounding and lying between the muscle fibers . Those of type one consist of a dense network of undulating collagen fibers lying on the surface of the muscle fibers (Fig. 1). The type two structures are made up of bundles of collagen fibers lying transversely between the muscle fibers, and binding them either to one another (Fig. 2), or to the neighbouring blood vessels. In a substantial number of these, globular elements are to be found, whereas in others, elastin-like material has been observed. The ends of the collagen fibers in these bundles become separated into branches, which diverge and become entwined with the sarcolemmic reticulum on the surface of the muscle fibers (Fig. 3). Apart from the collagen bundles between the myofibers, single
Correspondence to: V. Vasilev
)!I£ SEMPER
Ann Anat (1995) 177: 85 - 87 Gustav Fischer Verlag Jena
collagen fibers running in various directions and binding contiguous myofibers to each other and to nearby blood vessels were also seen. These fibers were assigned to the third type of endomysial collagen structure (Fig. 3). In some places they are closely bound to each other by their own branches, thus building up a loose reticulum. Their attachment to the muscle fibers is similar to that of the collagen fibers in the bundles.
Fig. 1. Sarcolemmic reticulum (SR) of collagen fibers on the surface of a muscle fiber (M). x4610
Fig. 2. Collagen bundles (B) connecting two contiguous muscle fibers (M). Within these bundles globular bodies of variable size can be seen (arrows). x2270
Fig. 3. Collagen bundles (B) and single collagen fibers (F) binding muscle fibers (M) to one another and to an adjacent capillary (C). x1500
86
The results obtained point to a three-dimensional endomysial collagen architecture, comprising three types of interrelated structure. The sarcolemmic reticulums covering individual myofibers play an essential role in this formation. Because of the mechanical resistance of collagen, they distribute the tensile forces during contraction and passive stretching of a muscle evenly, and thus prevent overstretching of the muscle fibre. On the other hand, owing to the undulating configuration of the constituent collagen fibers, these structures may also function as elastic system, promoting the relaxation of the muscle cell and assuming the role of shock-absorber in the event of a sudden contraction or strain. The other two types of endomysial collagen structure, i. e. the collagen bundles and the individual collagen fibers, bind the sarcolemmic networks of adjacent myofibers to one another or to the vascular walls. In this
fashion they contribute to the structural and functional integration of the individual muscle fibers as well as to the maintenance of an optimal blood flow through the muscles themselves.
References Borg T, Caulfield J (1980) Morphology of connective tissue in skeletal muscle. Tissue and Cell 12: 197- 207 Borg T, Sullivan T, Ivy J (1982) Functional arrangement of connective tissue in striated muscle with emphasis on cardiac muscle. Scanning Electron Microsc 4: 1775 -1784 Rowe R (1981) Morphology of perymysial and endomysial connective tissue in skeletal muscle. Tissue and Cell 13: 681 - 690 Accepted September 18, 1993
87