Laryngeal muscles as highly specialized organs in airway protection, respiration and phonation

• Published in: Handbook of Behavioral Neuroscience Vol. 19; pp. 13 - 21
• Main Author: Hoh, Joseph F.Y.
• Format: Book Chapter
• Language: English
• Published: Elsevier Science & Technology 2010
• Subjects: comparative physiology; contraction; laryngeal muscle; larynx; muscle allotype; muscle fiber types; myosin heavy chain; respiration; scaling; vocalization; myosin heavy chain; scaling; Ta-V: vocalis division of thyroarytenoid muscle; CT: cricothyroid muscle; vocalization; Ta: thyroarytenoid muscle; Ta-X: external division of thyroarytenoid muscle; muscle fiber types; respiration; MyHC: myosin heavy chain; comparative physiology; larynx; LCA: lateral cricoarytenoid muscle; EO: extraocular (myosin heavy chain); eo: extraocular (muscle fiber type); PCA: posterior cricoarytenoid muscle; contraction; IA: interarytenoid muscle; laryngeal muscle; muscle allotype; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis
• ISBN: 0123745934; 9780123745934
• ISSN: 1569-7339
• DOI: 10.1016/B978-0-12-374593-4.00002-4

Laryngeal muscles are a distinct allotype, differing from other muscles with respect to embryological origin and initiators (upstream activators) of myogenesis. They are endowed with a capacity to express a wider range of myosin heavy chains (MyHCs) than limb muscles. This includes extraocular (EO or 2L), 2B, 2X, 2A and slow MyHCs, generating fibers with decreasing speeds of contraction. MyHC expression and fiber-type profiles in laryngeal muscles show within-species and between-species variations. Within species, the vocal fold adductor, thyroarytenoid muscle (Ta), including the vocalis division that modulates vocal fold function, has faster fibers than the posterior cricoarytenoid muscle (PCA), the abductor, which has faster fibers than the vocal fold tensor, cricothyroid muscle (CT). Between species, small animals have faster muscle fibers than larger animals: EO MyHC is expressed in the Ta of rat and rabbit, but not in cat, dog, baboon, human, horse or cattle, while 2B MyHC is expressed in laryngeal muscles of cat and dog, but not their limb muscles. In the baboon, human, horse and cattle, only fibers expressing 2X, 2A and slow MyHCs are found. The CT only has fiber types found in limb muscles of the same species. Scaling considerations suggest that between-species variations in laryngeal muscle fiber types are evolutionary adaptations in response to changes in body mass and respiratory frequency. Within-species variations in fiber types ensure that protective closure of the glottis is always faster than movements regulating airflow during respiration. In common with muscles of other allotypes, laryngeal muscles are subjected to neural and hormonal regulation.