Electron microscopy, myelin structure

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

Enhanced lysosomal storage of phospholipids due to the inhibition of phospholipases is another special form of hepatic steatosis. The hepatocytes are enlarged and exhibit a distinctive foamy lucency of the cytoplasm. Crystalline inclusions and an agglomeration of myelin structures are visible in the lysosomes by electron microscopy. Mallory bodies may also be found. This idiosyncratic metabolic liver damage may even develop into cirrhosis, (s. p. 545) (s. tab. 31.4)... 

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