Correct answer:

Injury to the axon and myelin sheath without disruption of the continuity of its perineural sheath. The axon distal to the lesion degenerates (Wallerian degeneration) and regrowth of the axon occurs from the node of Ranvier proximal to the injury. As the sheath is intact, the correct axon will grow into its original nerve ending. The rate of regeneration is approximately 1 mm/day; therefore, the time to recovery depends upon the distance between the injury and the end organ.