A histological section of peripheral nerve stained with osmium tetroxide shows a dark ring around each myelinated axon with a central pale region. The dark ring represents which structure?
- A Endoneurium — collagen fibers around individual axons
- B Perineurium — multilayered barrier around the nerve fascicle
- C Myelin sheath — osmium-stained lipid-rich Schwann cell wraps ✓
- D Axolemma — the plasma membrane of the axon
Correct answer: C. Myelin sheath — osmium-stained lipid-rich Schwann cell wraps
Explanation
Osmium tetroxide is a lipid-fixing stain that blackens lipid-rich membranes. The myelin sheath, formed by concentric lamellae of Schwann cell membrane (rich in sphingomyelin and cholesterol), stains intensely black with osmium. The central pale region is the axon, which has relatively less lipid. The endoneurium (fine collagen) and perineurium are not stained black by osmium. This technique allows precise identification and measurement of myelin thickness (g-ratio) in nerve pathology studies.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.