Wallerian degeneration is initiated in which nerve injuries?

• A. Axonotmesis and Neurotmesis
• B. Neurapraxia
• C. Only Neurapraxia
• D. Only Axonotmesis

Answer: (A)

Wallerian degeneration happens when the axon is disrupted and separated from the neuron's cell body, so the distal segment degenerates. This occurs in injuries where the axon is damaged or severed, such as axonotmesis and neurotmesis. In axonotmesis, the axon and myelin distal to the injury degenerate, but the endoneurial tubes often remain intact, allowing potential regrowth along those pathways. In neurotmesis, there is complete disruption including the connective tissue coverings, so distal degeneration occurs and natural regrowth is unlikely without repair. Neurapraxia, on the other hand, involves a temporary conduction block with an intact axon, so there is no Wallerian degeneration distally.