Fiber composition of the recurrent laryngeal nerve after experimental vagotomy and sympathectomy. A qualitative study by light and electron microscopy.

A qualitative study of the nerve fiber composition of the recurrent laryngeal nerve of the rat was performed by light and electron microscopy. Various surgical denervation procedures were employed to determine the origin of the variously sized myelinated fibers and the unmyelinated axons present within the nerve. After extracranial vagotomy all myelinated fibers degenerated, whereas some unmyelinated axons remained intact. Intracranial vagotomy on the other hand revealed that about 70% of the small (1.5-4.0 micron) myelinated fibers were unaffected, as were many unmyelinated axons. After sympathectomy, both kinds degenerated but normal unmyelinated axons could be found. Thus, the majority of the small myelinated fibers are afferent sensory fibers whose cell bodies are located in the vagal ganglia at the base of the skull. The medium and large myelinated fibers represent efferent neurons originating from the brain stem. The unmyelinated fibers emanate from at least three different sites, viz. the brain stem, the sensory vagal ganglia and finally the ganglia of the cervical sympathetic nerve trunk.