Sections to be stained for myelin should be cut at

• A. 10-15 nm
• B. 0.5-1 μm
• C. 20-40 μm
• D. 100-200 μm

Answer: (A)

For visualizing the detailed, ultrastructural arrangement of myelin, sections must be extremely thin so electrons can pass through and produce a clear image. This is a situation best served by transmission electron microscopy, which uses ultrathin sections on the order of nanometers. Cutting at about 10–15 nanometers allows the electron beam to penetrate the specimen and resolve the multiple myelin lamellae that give the sheath its characteristic architecture. Thicker sections, in the micrometer range, are used for light microscopy and would not reveal the fine lamellar structure of myelin. That’s why ultrathin, nanometer-scale sections are the appropriate choice for studying myelin at the ultrastructural level.