Anatomy and Fiber Type Composition of Human Interarytenoid Muscle

Abstract

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.

Sarcomeric Myosin Expression in the Tongue Body of Humans, Macaques and Rats

“…Expression of developmental MHC isoforms was approximately 0.3% in humans and macaques and 0.05% in rats. Similar limited expression of developmental MHC has been demonstrated in many head and neck muscles by PCR and IHC Sundman et al, 2004;Tellis et al, 2004]. Detection of developmental MHC in these muscles is expected to be below the detection threshold of silver-or Coomassiestained protein gels, consistent with the general observation that these isoforms are not identified by electrophoresis in adult muscle.…”

Laryngeal muscle responses to mechanical displacement of the thyroid cartilage in humans

“…In conclusion, although other receptors may mediate laryngeal sensory feedback during vocalization, such as muscle spindles in the human interarytenoid muscle (28) and mechanoreceptors in the laryngeal mucosa (12), we speculate that the short-latency sternothyroid responses found here provide evidence that spindles in extrinsic laryngeal muscles might provide sensory feedback regarding changes in laryngeal height. Possibly the rapid changes in laryngeal height, which occur during pitch changes (14), could generate somatosensory feedback for laryngeal control during voice production.…”

“…The presence of muscle spindles in the intrinsic laryngeal muscles in humans is controversial (19,23). One report found muscle spindles in the interarytenoid (28), others reported spindles in the thyroarytenoid muscle (4,5,24), whereas a more recent study failed to confirm the presence of spindles in the thyroarytenoid muscle (8).…”

Myosin Heavy Chain-2b Transcripts and Isoform Are Expressed in Human Laryngeal Muscles

“…In some studies, only the 3 major MyHC isoforms (MyHC-1, -2a and -2x) were found [Wu et al, 2000a;Li et al, 2004;Tellis et al, 2004]. Similarly, even the unloaded maximal shortening velocities (V o ) of laryngeal type 1, 2a and 2x fibres were found to be similar to those of the limb muscles [D'Antona et al, 2002;Sciote et al, 2002].…”