Fiber components of the recurrent laryngeal nerve in the cat

Experimental neuroanatomical methods were employed in 21 adult cats to determine 1) the number and size of myelinated motor and sensory fibers in the recurrent laryngeal nerve (RLN), and 2) the fiber components originating in the nucleus ambiguus (NA) and retrofacial nucleus (RFN) of the brain stem. Intracranial transection of the X and XI cranial nerves and selective destruction of the NA or RFN were the experimental lesions inflicted in order to obtain the following results. About 55% (312) of the right RLN (565 fibers) is composed of myelinated motor nerve fibers which measure 4 mu - 9 mu in diameter. Nine percent come from the RFN and are smaller (4-6 mu) than the 46% which emanate from the NA and measure 6-9 mu in diameter. The remaining 45% of the RLN is made up of sensory neurons which can be divided into three groups. 1) The largest numerical group (32%) is very small in caliber (1-3 mu) and supplies extralaryngeal regions (trachea, esophagus). 2) The intermediate size fiber group (4-9 mu) comprises 11% of the RLN and probably supplies the subglottic mucosa. 3) The smallest group (2%) of sensory fibers is the largest in diameter (10-15 mu) and may represent either the innervation of muscle spindles or afferents from the superior laryngeal nerve coursing down into the chest.