Effect of denervation on primate laryngeal muscles: a morphologic and morphometric study.

Primate intrinsic laryngeal muscles studied consisted of Type I and Type II fibres. Type II fibres were larger than Type I fibres. The coefficient of variance of these muscles suggested that the fibre-size variation was similar in all of these muscles. Denervation resulted in shrinking of Type II fibres at two weeks in all the muscles, while at four weeks the thyroarytenoid showed an inflammatory reaction and far greater reduction in size than the other muscles. At eight weeks, however, all the muscles were fibrosed. We conclude that laryngeal muscles begin to show evidence of denervation at two weeks and are fibrosed in eight weeks. The thyroarytenoid muscle showed inflammatory degeneration, while the posterior cricoarytenoid and cricothyroid muscles showed classical changes of denervation. These findings should have clinical significance in the timing of reinnervation procedures.