RESUMO
BACKGROUND AND OBJECTIVES: Pharyngoesophageal musculature plays an important role in swallowing, and prevents aspiration and supraesophageal reflux. These muscles are closed during the resting state and opens with swallowing to allow the passage of food. In this study, the histochemical characteristics of the upper esophageal sphincter muscles in human were investigated. MATERIALS AND METHODS: Muscle samples from the inferior pharyngeal constrictor, cricopharyngeus, upper esophageal muscle and sternocleidomastoid (SCM) muscle were obtained from the healthy portion of nine laryngectomized specimen. We used the H&E staining for identifying the gross anatomy of these muscles, and the myofibrillar ATPase staining and the NADH-TR staining for differentiating the muscle fiber type. RESULTS: Analysis of the muscle fiber types of the upper esophageal sphincter muscle revealed a predominance of type I in the cricopharyngeus (78.9%) and the upper esophageal muscle (85.2%), and type II in the inferior pharyngeal constrictor muscle (80%). In the SCM muscle, the percentage of each fiber type was almost the same. The proportion of oxidative fibers within these muscles correlated well to that of the type I fibers. CONCLUSION: The distribution of the type I fibers tended to be higher in the upper esophageal muscle than in the inferior pharyngeal constrictor. These findings about fiber types represents well the physiological features of each muscle, i.e. the inferior pharyngeal constrictors are capable of short rapid contraction and the upper esophageal muscles are capable of slow rhythmic movement.