In nerve histology, Wallerian degeneration after axon injury is characterised by which sequence of events distal to the injury site?
- A Schwann cell death → myelin breakdown → axon swelling → chromatolysis
- B Axon fragmentation → myelin breakdown by Schwann cells and macrophages → Schwann cell proliferation forming bands of Büngner ✓
- C Retrograde degeneration → cell body hypertrophy → axon sprouting proximal to injury
- D Immediate chromatolysis → axon regeneration at 100 mm/day
Correct answer: B. Axon fragmentation → myelin breakdown by Schwann cells and macrophages → Schwann cell proliferation forming bands of Büngner
Explanation
Wallerian degeneration (anterograde degeneration) distal to a nerve injury: within 24–48 hours the axon begins to fragment; myelin breaks down and is phagocytosed by Schwann cells and recruited macrophages; Schwann cells de-differentiate and proliferate to form cylindrical bands of Büngner within the endoneurial tube, guiding regenerating axons. Chromatolysis (cell body changes) occurs retrograde and represents the cell body response to injury, not a primary event in Wallerian degeneration. Regeneration rate is approximately 1–4 mm/day, not 100 mm/day.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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