Patterns of reinnervation and motor unit recruitment in human hand muscles after complete ulnar and median nerve section and resuture.

Abstract

If we want to tie a shoelace, write a letter, eat, or play a musical instrument, we are confronted with the need to control our hand muscles precisely. Our ability to co-ordinate these and many other fine movements is generally assumed to result from direct corticospinal connections to the motoneurons innervating the hand muscles' 2 and from an orderly recruitment of motoneurons from small to large within each spinal motor pool.34One notable exception to this recruitment pattern occurred after resuture of a completely severed ulnar nerve in the forearm. Normal motor unit twitch amplitudes were re-established but the threshold force for recruitment of these reinnervated motor units remained abnormal. In addition to a disordered recruitment of motor units, these individuals showed poor motor co-ordination for fine movements.5 In these patients, the axons had been severed and so disconnected from a pathway to their peripheral end organs. As the ulnar nerve contains axons which innervate several intrinsic hand muscles, many muscles were denervated. During regeneration, the axons had to grow across the suture line and along the endoneurial tubes to innervate the denervated muscle fibres

Increased intensity and reduced frequency of EMG signals from feline self-reinnervated ankle extensors during walking do not normalize excessive lengthening

“…Another possible explanation for the observed decrease in the myoelectric signal frequency could be related to inappropriate reinnervation of muscle fibers by regenerating motoneuron axons (English 2005; Thomas et al 1987). Since this explanation could only explain the frequency decrease in LG due to its possible inappropriate reinnervation by small SO motoneurons but not the frequency decrease in self-reinnervated SO inappropriately innervated by large, on average, LG motoneurons, this explanation does not appear probable.…”

Experimental approaches to promote functional recovery after severe peripheral nerve injuries

“…Although, there is evidence that regenerating axons preferentially reinnervate motor endoneurial tubes leading to appropriate muscle targets [32][33][34], inability of motor axons to discriminate between their original and inappropriate denervated muscles severely compromises recovery of function [35][36][37][38]. Regeneration of axons across the surgical site is slow and occurs in a "staggered" fashion requiring up to 2 weeks to regenerate across the surgical site [39].…”

Reflex excitability of facial motoneurons at onset of muscle reinnervation after facial nerve palsy

“…4,5,8,26 The presence of unintended muscle activity during voluntary or reflex movements is one of the factors that may complicate recovery after nerve regeneration. This occurs in part because of ephaptic transmission or abnormal axonal branching at the point of the lesion, but enhancement of motoneuronal excitability related to deafferentation and synaptic reorganization may also be important.…”