Laryngeal muscle fibre types

Abstract

The internal laryngeal muscles have evolved to subserve the highly specialized functions of airways protection, respiration, and phonation. Their contractile properties, histochemistry, biochemical properties, myosin heavy chain (MyHC) expression and their regulation by nerves and hormones are reviewed and compared with limb muscle fibres. Cricothyroid, the vocal cord tensor, is limb-like in MyHC composition and fibre type properties, while the vocal fold abductor and adductors are allotypically different, with capacity for expressing an isoform of MyHC that is kinetically faster than the fastest limb MyHC. In rats and rabbits the faster isoform is the extraocular (EO) MyHC, while in carnivores, it is the IIB MyHC. These adaptations enable the abductor and adductor muscles to remain always faster than the cricothyroid as the latter changes in speed during evolution to match changing metabolic and respiratory rates in relation to scaling with body mass. Such phylogenetic plasticity is vital to the airways protection and respiratory functions of these muscles. The posterior cricoarythenoid, the abductor muscle, is tonically driven during expiration, and consequently has a slower fibre type profile than the principal adductor, the thyroarythenoid. The human thyroarythenoid appears not to express EO or IIB MyHC significantly, but is unique in expressing the slow-tonic MyHC. The concepts of allotype and phylogenetic plasticity help to explain differences in fibre type between limb and laryngeal muscles and between homologous laryngeal muscles in different species. Laryngeal muscle fibres exhibit physiological plasticity as do limb muscles, being subject to neural and hormonal modulation.

Avaliação da performance vocal antes e após a vibração sonorizada de língua

“…As fibras musculares da laringe exibem plasticidade fisiológica como os músculos esqueléticos, também sendo sujeitos à modulação neural e hormonal. Esta constatação favorece a aplicação das mesmas considerações aos músculos da fala e aos músculos esqueléticos (6) . Alguns autores (7) recomendam cautela na prescrição do tempo de performance de vibração sonorizada de língua/lábios para os diferentes gêneros, evitando assim, possíveis lesões ao sistema fonador.…”

Expression of eight distinct MHC isoforms in bovine striated muscles:evidence for MHC-2B presence only in extraocular muscles

“…In thyreoarytenoideus, a fourth MHC isoform was present and was identified as MHC-Neo. The expression of an additional MHC isoform is a typical feature of thyreoarytenoideus as discussed by Hoh (2005) and may need further investigation.…”

“…Since MHC-2B might be expressed also in laryngeal muscles (see for a review Hoh, 2005), we extended the analysis to bovine laryngeal muscles. Results are shown in Fig.·5.…”

“…In the present study, we aimed to demonstrate whether MHC-2B protein is present in bovine muscles and to extend the investigation to laryngeal muscles, a group of muscles where expression of MHC-2B can be expected. As recently reviewed by Hoh (2005), laryngeal muscles and, in particular, thyreoarytenoideus muscle express, in several species, MHC isoforms different from those found in the limb skeletal muscles. In rat and rabbit, thyreoarytenoideus muscle expresses MHC-2B and MHC-Eo (extraocular); there is also evidence in favour of the presence of MHC-2B in cat (Hoh, 2005) and possibly also in dog (Wu et al, 2000).…”

“…As recently reviewed by Hoh (2005), laryngeal muscles and, in particular, thyreoarytenoideus muscle express, in several species, MHC isoforms different from those found in the limb skeletal muscles. In rat and rabbit, thyreoarytenoideus muscle expresses MHC-2B and MHC-Eo (extraocular); there is also evidence in favour of the presence of MHC-2B in cat (Hoh, 2005) and possibly also in dog (Wu et al, 2000). In bovine thyreoarytenoideus muscle, fibres show an unusual histochemical profile (Mascarello and Veggetti, 1979) and this suggests the presence of some isoforms different from those present in limb muscles.…”