NEUROMUSCULAR ORGANIZATION OF THE HUMAN UPPER ESOPHAGEAL SPHINCTER

The upper esophageal sphincter (UES) is a key component of swallowing, and yet, its anatomy and function are still incompletely understood. The UES is a functional entity that is composed of three muscles: the cricopharyngeal (CP) muscle, the inferior pharyngeal constrictor (IPC) muscle, and the upper esophageal (UE) muscle. This study compared the anatomy of the three muscles of the UES in nine human autopsy specime ns. The variables examined included the pattern of motor end plates (a cetylcholinesterase stain), the proportion of fast-and slow-twitch mus cle fibers (myofibrillar adenosinetriphosphatase), and the details of their nerve supply (Sihler's stain). The results demonstrated that eac h variable is different in the three muscles. For example, the IPC mus cle is innervated by the pharyngeal plexus, the CP muscle by both the pharyngeal plexus and the recurrent laryngeal nerve (RLN), and the UE muscle by the RLN. The LPC and CP muscles showed distinct motor end pl ate bands, while the horizontal part of the CP muscle also contained s mall and randomly scattered end plates. This latter pattern was presen t throughout the UE muscle. Analysis of the muscle fiber types of the UES revealed a type I (slow) predominance (89%) in the CP and UE muscl es and a type II (fast) predominance (62%) in the IPC muscle. However, the IPC muscle is composed of two layers: a fast, thick, outer layer (90% type II) and a slow, thin, inner layer (85% type I). The implicat ions of these findings for the diagnosis and treatment of UES dysfunct ion will be discussed.