Muscle Fiber Type Composition and Effects of Vocal Fold Immobilization on the Two Compartments of the Human Posterior Cricoarytenoid: A Case Study of Four Patients

Abstract

SummaryThe human posterior cricoarytenoid (PCA) muscle is divided into two compartments, the vertical and horizontal bellies, which contain differences in their myosin heavy chain (MyHC) composition. Using immunohistochemical techniques on whole PCA samples, this study provides a more thorough description of the fiber type composition of entire bellies of the PCA. Four patients provided complete PCA samples containing both compartments of their right and left sides; two with unilaterally immobilized vocal folds. The horizontal belly had 80% slow (type I) fibers and 20% fast (type II) fibers. The vertical belly contained equal amounts of slow and fast fibers (~55%:45%); clearly distinguishing between two compartments. Atrophy of muscle fibers and fiber type grouping were also present in both normal and affected subjects; providing no clear confirmation of the clinical findings of vocal fold immobilization. Further study of the PCA muscle from patients with unilaterally immobilized vocal folds is needed.

Anatomy and Fiber Type Composition of Human Interarytenoid Muscle

“…The fiber type distribution, at least in simple muscle spindles in smaller mammals, usually consists of 1 bag1 fiber, 1 bag2 fiber, and 2 or more chain fibers. In previous investigations, we were unable to identify muscle spindles in human PCA 10 and TA 11 muscles. In the current study, however, muscle spindles were easily identified in human IA muscle, at an average of 7 spindles per muscle.…”

“…11 Likewise, no spindle structures were identified in the PCA muscle. 10 In the IA muscle, however, we were able to identify muscle spindles easily, at an average of 7 spindles per muscle. Some of these spindles had complex anatomy, in that for part of their length they shared a connective capsule with another spindle.…”

“…A variety of new investigative methods can be used on normally functioning laryngeal muscle to biochemically isolate contractile and regulatory proteins 4,5 and gene message (m-RNA), 6 to determine the physiological properties of single muscle fibers or fiber bundles, 7,8 and to establish fiber type amount and distribution from frozen tissue sections. [9][10][11] These techniques taken together give a more complete estimate of how intrinsic laryngeal muscles behave physiologically during laryngeal function. This information forms an important basis for characterization of normal contraction speeds and fatigue rates, and whether these characteristics change in voice disorders such as vocal fold paralysis, paresis, atrophy, and muscle tension dysphonia.…”

“…20 We recently attempted to confirm the results of Sanders et al 20 by immunohistochemical staining with antibodies reactive for neonatal and tonic myosin, but we were unable to identify muscle spindles in either the TA or PCA muscles. 10,11 Given the close proximity of muscle fiber cells to the vocal fold and the abundant connective tissue component of TA muscle, it is possible to confuse several isolated skeletal muscle fibers associated with muscle connective tissue with a true muscle spindle. Staining with tonic and neonatal myosin easily separates true spindles from structures that morphologically appear to be spindles after routine cell staining.…”

Specialized Cranial Muscles: How Different Are They from Limb and Abdominal Muscles?

“…In contrast, the jaw-closing muscles have functions, anatomy and fiber types that vary tremendously between species. Laryngeal muscles have more modest variability in anatomy, perhaps more significant variability in function and their fiber type properties are currently under investigation [Brandon et al, 2003].…”