Skip to main content
PMC home page
The Journal of Biophysical and Biochemical Cytology logoLink to The Journal of Biophysical and Biochemical Cytology
. 1957 Sep 25;3(5):725–748. doi: 10.1083/jcb.3.5.725

ELECTRON MICROSCOPE AND LOW-ANGLE X-RAY DIFFRACTION STUDIES OF THE NERVE MYELIN SHEATH

H Fernández-morán 1, J B Finean 1
PMCID: PMC2224112  PMID: 13475388

Abstract

1. A close correlation has been obtained between high resolution electron microscopy and low-angle x-ray diffraction studies of the myelin sheath of frog and rat peripheral and central nerves. Extensive studies were performed by application of both techniques to the same specimens, prepared for examination by OsO4 or KMnO4 fixation, and embedding either in methacrylate or in gelatin employing a new procedure. Controlled physical and chemical modifications of the myelin sheath prior to fixation were also investigated. 2. A correspondence was established between the layer spacings observed in electron micrographs and the fundamental radial repeating unit indicated by the low-angle x-ray diffraction patterns. The variations in relative intensities of the low-angle x-ray reflections could be related to the radial density distributions seen in the electron micrographs. 3. An analysis of the preparation procedures revealed that OsO4 fixation introduces a greater shrinkage of the layer spacings and more pronounced changes in the density distribution within the layers than KMnO4 fixation. The effects of methacrylate and gelatin embedding are described, and their relative merits considered in relation to the preservation of myelin structure by OsO4 fixation. 4. The experimental modifications introduced by freezing and thawing of fresh whole nerve are described, particularly the enhancement of the intermediate lines and the dissociation of the layer components in the myelin sheath. A characteristic collapsing of the radial period of the sheath is observed after subjecting fresh nerve trunks to prolonged and intense ultracentrifugation. 5. Controlled extraction of fresh nerve with acetone at 0°C., which preferentially removes cholesterol, produces characteristic, differentiated modifications of the myelin sheath structure. Electron microscopy reveals several types of modifications within a single preparation, including both expanded and collapsed layer systems, and internal rearrangements of the layer components. Alcohol extraction leads to a more extensive structural breakdown, but in certain areas collapsed layer systems can still be observed. The components of the lipide extracts could be identified by means of x-ray diffraction. These modifications emphasize the importance of cholesterol in the myelin structure, and disclose a resistance of the dense osmiophilic lines to lipide solvents. 6. The significance of these structures is discussed in relation to present concepts of the molecular organization of myelin. The available evidence is consistent with the suggestion that the primary site of osmium deposition is at the lipoprotein interfaces and that the light bands probably represent regions occupied by lipide chains. The electron microscope and x-ray diffraction data also indicate the possibility of a regular organization within the plane of the layers, probably involving units of 60 to 80 A. The myelin sheath is regarded as a favourable cell membrane model for detailed analysis by combined application of x-ray diffraction and electron microscopy.

Full Text

The Full Text of this article is available as a PDF (3.4 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. 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]
  2. FINEAN J. B. Further observations on the structure of myelin. Exp Cell Res. 1953 Sep;5(1):202–215. doi: 10.1016/0014-4827(53)90106-2. [DOI] [PubMed] [Google Scholar]
  3. FINEAN J. B., MILLINGTON P. F. Effects of ionic strength of immersion medium on the structure of peripheral nerve myelin. J Biophys Biochem Cytol. 1957 Jan 25;3(1):89–94. doi: 10.1083/jcb.3.1.89. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. FINEAN J. B. The effects of osmium tetroxide fixation on the structure of myelin in sciatic nerve. Exp Cell Res. 1954 May;6(2):283–292. doi: 10.1016/0014-4827(54)90175-5. [DOI] [PubMed] [Google Scholar]
  5. FINEAN J. B. The role of water in the structure of peripheral nerve myelin. J Biophys Biochem Cytol. 1957 Jan 25;3(1):95–102. doi: 10.1083/jcb.3.1.95. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. FINEAN J. B. X-ray analysis of the structure of peripheral nerve myelin. Nature. 1954 Mar 20;173(4403):549–550. doi: 10.1038/173549a0. [DOI] [PubMed] [Google Scholar]
  7. Geren B. B., Raskind J. Development of the Fine Structure of the Myelin Sheath in Sciatic Nerves of Chick Embryos. Proc Natl Acad Sci U S A. 1953 Aug;39(8):880–884. doi: 10.1073/pnas.39.8.880. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Geren B. B., Schmitt F. O. THE STRUCTURE OF THE SCHWANN CELL AND ITS RELATION TO THE AXON IN CERTAIN INVERTEBRATE NERVE FIBERS. Proc Natl Acad Sci U S A. 1954 Sep;40(9):863–870. doi: 10.1073/pnas.40.9.863. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. 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]
  10. 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]
  11. PALADE G. E. A study of fixation for electron microscopy. J Exp Med. 1952 Mar;95(3):285–298. doi: 10.1084/jem.95.3.285. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. PALADE G. E. An electron microscope study of the mitochondrial structure. J Histochem Cytochem. 1953 Jul;1(4):188–211. doi: 10.1177/1.4.188. [DOI] [PubMed] [Google Scholar]
  13. PORTER K. R., BLUM J. A study in microtomy for electron microscopy. Anat Rec. 1953 Dec;117(4):685–710. doi: 10.1002/ar.1091170403. [DOI] [PubMed] [Google Scholar]
  14. SCHMITT F. O. The ultrastructure of the nerve myelin sheath. Res Publ Assoc Res Nerv Ment Dis. 1950;28:247–254. [PubMed] [Google Scholar]

Articles from The Journal of Biophysical and Biochemical Cytology are provided here courtesy of The Rockefeller University Press

RESOURCES