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

1957 ◽  
Vol 3 (5) ◽  
pp. 725-748 ◽  
Author(s):  
H. Fernández-morán ◽  
J. B. Finean
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Electron Micrographs ◽  
Myelin Sheath ◽  
High Resolution Electron Microscopy ◽  
Molecular Organization ◽  
X Ray Diffraction ◽  
Freezing And Thawing ◽  
X Ray ◽  
Myelin Structure

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.

scholarly journals SEQUENCES IN THE FORMATION OF CLOTS FROM PURIFIED BOVINE FIBRINOGEN AND THROMBIN: A STUDY WITH THE ELECTRON MICROSCOPE

1949 ◽  
Vol 90 (3) ◽  
pp. 225-232 ◽  
Author(s):  
Keith R. Porter ◽  
Clinton Van Zandt Hawn
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
X Ray Diffraction ◽  
X Ray ◽  
Physical Constants ◽  
Lateral Association ◽  
Fibrinogen Molecule

The observed sequences in the formation of clots from purified bovine fibrinogen and thrombin are described. Under the conditions of these experiments, it appears that fibrinogen molecules are polymerized by the action of thrombin to form needle-shaped, crystal-like protofibrils which then become aligned into fiber strands by lateral association. The integrity of the unit fibrils is maintained within the strand. A model of the fibrinogen molecule is proposed which may satisfy the reported physical constants, data from x-ray diffraction studies, and observations made upon electron micrographs.

Kinetic Study on the Formation of the Aragonite-Like Phase Ba(CuOx)1-Y(CO3)y

1995 ◽  
Vol 398 ◽  
Author(s):  
A. Tomasi ◽  
E. Galvanetto ◽  
F.C. Matacotta ◽  
P. Nozar ◽  
P. Scardi ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Thermal Analysis ◽  
High Resolution Electron Microscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Analysis Techniques ◽  
Formation Kinetics ◽  
Resolution Electron ◽  
Thermal Analysis Techniques ◽  
Kinetics Of

ABSTRACTA systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-500°C, under various atmospheres, by traditional thermal analysis techniques, high temperature X-ray diffraction and high resolution electron microscopy, has permitted to identify and characterise the formation kinetics of a new copper containing phase isomorphic to γ-BaCO3.

scholarly journals ELECTRON MICROSCOPE AND X-RAY DIFFRACTION STUDIES OF THE EFFECTS OF DEHYDRATION ON THE STRUCTURE OF NERVE MYELIN

1960 ◽  
Vol 8 (1) ◽  
pp. 13-29 ◽  
Author(s):  
J. B. Finean
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Diffraction Data ◽  
Intermediate Stage ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dense Line ◽  
Tissue Shrinkage ◽  
Frog Sciatic Nerve ◽  
Electron Microscope Data

The dehydration of frog sciatic nerve has been studied by allowing specimens to become partially or fully dried before fixation and preparation for electron microscopy. Low magnification electron micrographs of OsO4-fixed preparations showed marked tissue shrinkage which could be correlated quantitatively with the loss of water during the preliminary drying. KMnO4-fixation appeared to cause a rehydration of the dried tissue. Higher magnification electron micrographs of the OsO4-fixed preparations showed a sequence of modifications of the myelin layers which could be correlated with changes in the small-angle x-ray diffraction data which were recorded during drying. An intermediate stage of drying was characterised by a partial collapse of layers and a disappearance of the intraperiod dense line in some regions of the myelin sheath. Continuity between collapsed and non-collapsed layers was maintained throughout the sheath. The fully dried preparation showed two main modifications of the myelin layers. In many regions the layers (principal layers) resembled those of normal preparations, but showed an intensification and frequently a doubling of the intraperiod dense line. In addition, there was a very extensive system of fine (40 A periodicity) dense layers, some of which could be demonstrated to be continuous with the principal layers. In such cases it was observed that two of the fine layers were related to each principal layer. The correlation between diffraction data and electron microscope data is discussed, and some speculations are made concerning the molecular significance of the observations.

scholarly journals An electron microscopic and optical diffraction analysis of the structure of Limulus telson muscle thick filaments.

1982 ◽  
Vol 92 (2) ◽  
pp. 443-451 ◽  
Author(s):  
R W Kensler ◽  
R J Levine
Keyword(s):  
Electron Microscopy ◽  
Diffraction Analysis ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Thick Filaments ◽  
Diffraction Patterns ◽  
Cross Bridges

Long, thick filaments (greater than 4.0 micrometer) rapidly and gently isolated from fresh, unstimulated Limulus muscle by an improved procedure have been examined by electron microscopy and optical diffraction. Images of negatively stained filaments appear highly periodic with a well-preserved myosin cross-bridge array. Optical diffraction patterns of the electron micrographs show a wealth of detail and are consistent with a myosin helical repeat of 43.8 nm, similar to that observed by x-ray diffraction. Analysis of the optical diffraction patterns, in conjunction with the appearance in electron micrographs of the filaments, supports a model for the filament in which the myosin cross-bridges are arranged on a four-stranded helix, with 12 cross-bridges per turn or each helix, thus giving an axial repeat every third level of cross-bridges (43.8 nm).

Electron optical studies of the formation of vanadium pentoxide catalyst

1987 ◽  
Vol 45 ◽  
pp. 354-355
Author(s):  
A. Legrouri
Keyword(s):  
Electron Microscopy ◽  
Vanadium Pentoxide ◽  
High Resolution Electron Microscopy ◽  
X Ray Diffraction ◽  
Optical Studies ◽  
X Ray ◽  
Physicochemical Changes ◽  
Structural Correlation ◽  
Resolution Electron ◽  
Xrd Techniques

The oxides of vanadium, especially vanadium pentoxide, have been extensively studied because of their interesting physical properties particularly in catalysis. Vanadium pentoxide is generally used in the oxidation and ammoxidation of hydrocarbons.This catalyst has been prepared via the thermal decomposition of ammonium metavanadate (AMV) in air. Thermogravimetric analysis (TGA), infrared spectroscopy (IRS) and x-ray diffraction (XRD) techniques together with high resolution electron microscopy (HREM) and scanning electron microscopy (SEM) have enabled us to elucidate the physicochemical changes occurring during the decomposition process.According to TGA results, the decomposition of AMV commences at 150°C and is complete by 320°C leading to vanadium pentoxide by loss of ammonia and water with the formation of two intermediate compounds, namely at 190°C, ammonium bivanadate: (NH4)2V4 O11, and at 230°C, ammonium hexavanadate AHV: (NH4)2V6O16 . Samples for structural correlation studies were prepared by heating AMV in a stream of air for 2 hours at selected temperatures of 140, 190, 230, 320 and 400°C.

Fabrication of g-C3N4/Y-TiO2 Z-scheme heterojunction photocatalysts for enhanced photocatalytic activity

2021 ◽  
Author(s):  
SongSik Pak ◽  
KwangChol Ri ◽  
Chenmin Xu ◽  
Qiuyi Ji ◽  
Dunyu Sun ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Fourier Transform ◽  
Photocatalytic Activity ◽  
Electron Microscope ◽  
Photoelectron Spectroscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Electron

The g-C3N4/Y-TiO2 Z-scheme heterojunction photocatalysts were successfully synthesized. The powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscope, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used for...

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