The intraneural distribution of myelinated fibres in the equine recurrent laryngeal nerve.

The intraneural course of nerve fibres in the equine recurrent laryngeal nerve was investigated by partially ligating the nerve at a proximal site, and 3-8 weeks later, tracing the course and spatial relationships of intact and degenerating fibres along the distal stump. This nerve was chosen because of its great length, the fact that it is a nonbranching motor nerve and because of debate about the course of abductor and adductor nerve fibres in the recurrent laryngeal nerve. Six ponies were used and in each the recurrent nerve was partially ligatured about 20 cm from the larynx, using a fine silk suture. In all there was a clear separation of intact and degenerating fibres just distal to the suture, but they became mixed close to the point of innervation of the laryngeal muscles. The numbers of intact myelinated fibres remained similar along the partially denervated nerve segment. These results suggest that myelinated fibres mix within the recurrent laryngeal nerve and that focal lesions of this nerve should not result in denervation of individual laryngeal muscles.