THE INTRAMUSCULAR NERVE SUPPLY OF THE POSTERIOR CRICOARYTENOID MUSCLEOF THE DOG

The paired posterior cricoarytenoid (PCA) muscle has three separate mu scle bellies that differ in muscle fiber type (percentage of fast vs. slow twitch) and electromyelographic activity, and, in addition, produ ce different movements of the arytenoids when stimulated. An investiga tion of the innervation of the muscle was undertaken to demonstrate th e existence of separate functional units. The intramuscular nerve supp ly of the PCA from five sacrificed dogs were microdissected. The intra muscular nerves of three additional dogs were removed and stained for acetylcholinesterase, which differentiates axons bound for fast- and s low-twitch muscle, and sensory end organs. Three separate fascicles ar e described entering the PCA muscle from a single branch of the recurr ent laryngeal nerve. The three fascicles differ in axon type compositi on and in sensory, autonomic, and motor percentages, with the ratio of fast twitch to slow twitch varying from 0.78 to 1.5 to 1.7 (P < .05). This variation supports separate functional capabilities for the thre e muscle bellies of the PCA.