Neuromuscular compartments and fiber‐type regionalization in the human inferior pharyngeal constrictor muscle

Abstract

The inferior pharyngeal constrictor (IPC) muscle functions during swallowing, respiration, and vocalization. The most-caudal portion of the IPC is believed to be part of the functional upper esophageal sphincter (UES). We hypothesized that the caudal fibers of the human IPC may have enzyme-histochemical characteristics similar to those of the cricopharyngeus muscle, a major component of the UES. In this study, human IPC muscles obtained from autopsy were studied using Sihler's stain to examine innervation patterns, and using myofibrillar ATPase, NADH tetrazolium reductase (NADH-TR), and succinic dehydrogenase (SDH) techniques to investigate the distribution and oxidative capacity of the slow-(type I) and fast-(type II) twitch fibers in the muscle. The results showed that the human IPC consists of at least two neuromuscular compartments (NMCs): rostral and caudal. Each of the NMCs was innervated by a separate nerve branch derived from the pharyngeal branch of the vagus nerve. The rostral NMC is faster (39% type I, 61% type II) than the caudal NMC (70% type I, 30% type II). In addition, two histochemically-delineated fiber layers were identified in the human IPC: a slow inner layer (SIL) with predominantly type I fibers (66%), and a fast outer layer (FOL) with predominantly type II fibers (62%) (P Ͻ 0.01). However, the dimensions of both fiber layers and proportions of the muscle fiber types varied with the NMCs. Specifically, the ratio of the thickness of the SIL to FOL was ϳ2:1 for the caudal NMC and ϳ1:2 for the rostral NMC, respectively. In the SIL the type I fibers accounted for 84% for the caudal NMC and 69% and 44% for the lower and upper portions of the rostral NMC. In contrast, the type II fibers in the FOL accounted for 46% for the caudal NMC and 67% and 74% for the lower and upper portions of the rostral NMC, respectively (P Ͻ 0.01). The caudal NMC of the IPC shared histochemical characteristics with the cricopharyngeus muscle, in that it contained predominantly slow oxidative fibers. Overall, the caudal NMC and the SIL in the IPC had high NADH-TR and SDH activities. However, different patterns of oxidative enzyme activity were identified in both type I and type II fibers. This study provided histochemical evidence for the concept that the caudal NMC within the IPC contributes to the functional UES. In addition, the two histochemically-defined fiber layers in the IPC may be a specialized adaptation in humans to enable different upper-airway functions during respiration, swallowing, and speech. Anat

The Effects of Bolus Volume and Texture on Pharyngeal Pressure Events Using High-resolution Manometry and Its Comparison with Videofluoroscopic Swallowing Study

“…21 The inferior pharyngeal constrictor muscle is composed of mainly faster fiber (39% type 1, 61% type 2). 22 On the other hand, the cricopharyngeus muscle is 25-35 µm in diameter and is a small striated muscle. The fiber type is mainly highly oxidative, slow twitch type 1 fiber and a small portion of fast twitch type 2 (70% type I, 30% type II) 22,23 Therefore these narrow peaks should represent the pharyngeal peristalsis from the inferior pharyngeal constrictor muscle (mainly fast twitch fiber, type 2), and the broad peak should represent UES peak from the cricopharyngeus muscle (mainly slow twitch fiber, type 1).…”

“…22 On the other hand, the cricopharyngeus muscle is 25-35 µm in diameter and is a small striated muscle. The fiber type is mainly highly oxidative, slow twitch type 1 fiber and a small portion of fast twitch type 2 (70% type I, 30% type II) 22,23 Therefore these narrow peaks should represent the pharyngeal peristalsis from the inferior pharyngeal constrictor muscle (mainly fast twitch fiber, type 2), and the broad peak should represent UES peak from the cricopharyngeus muscle (mainly slow twitch fiber, type 1). To distinguish the shallow and broad peaks, we selected the channel that showed the maximal peak for narrow peaks and named it "low pharyngeal pressure," while we measured the broad peak and named it "UES peak."…”

Newly Revealed Cricothyropharyngeus Muscle in the Human Laryngopharynx

“…The NMCs in a muscle are usually defined first by regional differences in muscle fiber and tendon arrangement (English and Letbetter, 1982a;Richmond and Armstrong, 1988;Chanaud et al, 1991a;Segal et al, 1991;Zaretsky and Sanders, 1992;Sanders et al, 1994Sanders et al, , 1998Mu and Sanders, 1998b, 2008, separate intramuscular nerve branches supplying distinct regions (English and Letbetter, 1982a;Chanaud et al, 1991a;Segal et al, 1991;Sanders et al, 1994;Mu and Sanders, 1998a,b, 2000, 2007, 2008, separate motor endplate bands (Galvas and Gonyea, 1980;Sanders, 1998b, 2000), and histochemical fiber-type regionalization (English and Letbetter, 1982b;Richmond and Armstrong, 1988;Chanaud et al, 1991b;Mu and Sanders, 1998b, 2001, 2007. The NMCs can be arranged in-parallel (English and Letbetter, 1982a;Sanders et al, 1994;Mu and Sanders, 2000), in-series (Richmond and Armstrong, 1988;Mu and Sanders, 1998b), or both (Richmond et al, 1985).…”

“…The NMCs can be arranged in-parallel (English and Letbetter, 1982a;Sanders et al, 1994;Mu and Sanders, 2000), in-series (Richmond and Armstrong, 1988;Mu and Sanders, 1998b), or both (Richmond et al, 1985). The NMCs in the extraocular (Wasicky et al, 2000) and pharyngeal (Mu and Sanders, 2001, 2007Mu et al, 2007a,b) muscles can be organized into layers. The arrangement patterns of the NMCs appear to be related to the anatomical positions and physiological demands of the muscles.…”

“…Unfortunately, traditional anatomical methods usually fail to precisely determine the intramuscular neural patterns. To this end, Sihler's stain has been proved to be a reliable technique that clears muscle tissue, while counterstaining the nerves which can be traced from main trunk to the terminals (Sanders et al, 1994;Mu and Sanders, 1998a,b, 2000, 2001, 2007, 2008Ren and Mu, 2005).…”