Abstract
The structure of myelinated nerve fibres has been studied in the spinal cord and optic nerve of the tadpoles of Xenopus laevis. Potassium permanganate-fixed material was examined with the electron microscope. The myelin sheath itself is made up of spirally arranged lamellae in which the intraperiod and dense lines alternate. Inside the myelin sheath an inner cytoplasmic process surrounds the axon and where the external surfaces of its bounding membrane come together an internal mesaxon is formed. The intraperiod line begins within the mesaxon and the dense line usually begins in the same region by apposition of the cytoplasmic surfaces of the membrane. The width of each lamella is 140 A. The outer line in the sheath is the dense line and this terminates in a tongue where the cytoplasmic surfaces of the myelin-forming glial cell separate. Thus, central myelin in Xenopus tadpoles is arranged in the same way as peripheral myelin, the only difference being that in central fibres, cytoplasm on the outside of the sheath is confined to that present in the tongue. For this reason adjacent central sheaths come into apposition without any intervening material being present. When this occurs an intraperiod line is formed between them.
Full Text
The Full Text of this article is available as a PDF (1.2 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- BEN GEREN B. The formation from the Schwann cell surface of myelin in the peripheral nerves of chick embryos. Exp Cell Res. 1954 Nov;7(2):558–562. doi: 10.1016/s0014-4827(54)80098-x. [DOI] [PubMed] [Google Scholar]
- DE ROBERTIS E., GERSCHENFELD H. M., WALD F. Cellular mechanism of myelination in the central nervous system. J Biophys Biochem Cytol. 1958 Sep 25;4(5):651–656. doi: 10.1083/jcb.4.5.651. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LUFT J. H. Permanganate; a new fixative for electron microscopy. J Biophys Biochem Cytol. 1956 Nov 25;2(6):799–802. doi: 10.1083/jcb.2.6.799. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LUSE S. A. Formation of myelin in the central nervous system of mice and rats, as studied with the electron microscope. J Biophys Biochem Cytol. 1956 Nov 25;2(6):777–784. doi: 10.1083/jcb.2.6.777. [DOI] [PMC free article] [PubMed] [Google Scholar]
- ROBERTSON J. D. Structural alterations in nerve fibers produced by hypotonic and hypertonic solutions. J Biophys Biochem Cytol. 1958 Jul 25;4(4):349–364. doi: 10.1083/jcb.4.4.349. [DOI] [PMC free article] [PubMed] [Google Scholar]