Correct answer:

Actual physical disruption of the peripheral nerve. Regeneration will take place provided the two nerve ends are not too far apart, but functional recovery will never be complete. Following the complete disruption of neurotmesis, the distal part of the severed nerve undergoes Wallerian degeneration. The medullary sheath is depleted of myelin and the axon cylinders vanish; the empty endoneural sheaths remain as tubules composed of proliferating neurilemmal cells. The proximal end of the nerve degenerates up to the first uninjured node of Ranvier. New axis cylinders proliferate from this point and grow into the empty neurilemmal tubules. However, there is no selection of tubules for the appropriate axon; the distal growth is governed solely by the position of the nerve fibres. Thus, with most mixed nerves, there is likely to be considerable wastage owing to regenerating fibres growing into endings which are functionless, i.e. motor nerve endings growing into sensory nerve endings and vice versa. Even when a motor nerve grows into a motor nerve ending it may not supply the original muscle and the patient will have to relearn the affected movement.