Abstract
1. The structure of the smooth muscle fibres in the longitudinal muscle coat of the body wall of Lumbricus terrestris has been investigated by phase contrast light microscopy and electron microscopy. 2. The muscle fibre is ribbon-shaped, and attached to each of its two surfaces is a set of myofibrils. These are also ribbon-shaped, and they lie with their surfaces perpendicular to the surfaces of the fibre, and their inner edges nearly meeting in the middle of the fibre. These fibrils are oriented at an angle to the fibre axis, and diminish greatly in width as they approach the edge of the fibre. The orientation of the set of fibrils belonging to one surface of the fibre is the mirror image of that of the set belonging to the other surface; thus, when both sets are in view in a fibre lying flat on one face, the fibre exhibits double oblique striation. A comparison of extended and contracted fibres indicates that as the fibre contracts, the angle made between fibre and fibril axes increases (e.g. from 5 to 30°) and so does the angle made between the two sets of fibrils (e.g. from 10 to 60°). 3. The myofibril, throughout its length, contains irregularly packed filaments, commonly 250 A in diameter, which are parallel to its long axis and remain straight in contracted muscles. Between them is material which probably consists of much finer filaments. Thus A and I bands are absent. 4. Bound to one face of each fibril, but not penetrating inside it, is a regularly spaced series of transverse stripes. They are of two kinds, alternating along the length of the fibril, and it is suggested that they are comparable to the Z and M lines of a cross-striated fibril. The spacing of these stripes is about 0.5 µ ("Z" to "Z") in extended muscles, and 0.25 µ in contracted muscles. A bridge extends from each stripe across to the stripeless surface of the next fibril.
Full Text
The Full Text of this article is available as a PDF (1.1 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- HANSON J., HUXLEY H. E. Structural basis of the cross-striations in muscle. Nature. 1953 Sep 19;172(4377):530–532. doi: 10.1038/172530b0. [DOI] [PubMed] [Google Scholar]
- HANSON J. Studies on the cross-striation of the indirect flight myofibrils of the blowfly Calliphora. J Biophys Biochem Cytol. 1956 Nov 25;2(6):691–710. doi: 10.1083/jcb.2.6.691. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGE A. J., HUXLEY H. E., SPIRO D. Electron microscope studies on ultrathin sections of muscle. J Exp Med. 1954 Feb;99(2):201–206. doi: 10.1084/jem.99.2.201. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HUXLEY A. F., NIEDERGERKE R. Structural changes in muscle during contraction; interference microscopy of living muscle fibres. Nature. 1954 May 22;173(4412):971–973. doi: 10.1038/173971a0. [DOI] [PubMed] [Google Scholar]
- HUXLEY A. F., TAYLOR R. E. Function of Krause's membrane. Nature. 1955 Dec 3;176(4492):1068–1068. doi: 10.1038/1761068a0. [DOI] [PubMed] [Google Scholar]
- HUXLEY H. E. Electron microscope studies of the organisation of the filaments in striated muscle. Biochim Biophys Acta. 1953 Nov;12(3):387–394. doi: 10.1016/0006-3002(53)90156-5. [DOI] [PubMed] [Google Scholar]
- HUXLEY H., HANSON J. Changes in the cross-striations of muscle during contraction and stretch and their structural interpretation. Nature. 1954 May 22;173(4412):973–976. doi: 10.1038/173973a0. [DOI] [PubMed] [Google Scholar]
- MARK J. S. An electron microscope study of uterine smooth muscle. Anat Rec. 1956 Jul;125(3):473–493. doi: 10.1002/ar.1091250306. [DOI] [PubMed] [Google Scholar]
- WEINSTEIN H. J., RALPH P. H. Myofilaments from smooth muscle. Proc Soc Exp Biol Med. 1951 Nov;78(2):614–615. doi: 10.3181/00379727-78-19158. [DOI] [PubMed] [Google Scholar]