Explains how osmium tetroxide staining makes the myelin sheath of peripheral nerve fibres appear black while axons stay pale. It describes how to recognise the stain in cross-section, where black rings each enclose a pale axon, and in longitudinal section, where black lines are interrupted at the nodes of Ranvier. It also names the endoneurium, perineurium and epineurium sheaths and warns against confusing myelinated fibres with unmyelinated ones.
Inside: 1 section · 1 min
Topic 122 of 127 in the MU Sofia syllabus for Cytology (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 86 words (1 min of reading).
In this note
Introduction
Introduction
Osmium tetroxide reacts with lipids, so it blackens the lipid-rich myelin sheath of peripheral nerve fibres.
Stain
Osmium tetroxide: myelin black, axons pale.
How to recognise it
Cross-section: black rings of different sizes, each with a pale axon in the centre.
Longitudinal section: black parallel lines, interrupted at the nodes of Ranvier.
Connective tissue sheaths: endoneurium around each fibre, perineurium around each fascicle, epineurium around the whole nerve.
Don't confuse it with: unmyelinated fibres, which have no black ring.
Theory: topic 66 (nerve fibres and myelin).
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