Thyroarytenoid muscle: Functional subunits based on morphology and muscle fiber typing in cats

Using parvalbumin immunohistochemistry to determine the distribution of mus cle fiber types in the feline thyroarytenoid muscle (TA), we clearly distin guished the vocalis (with predominance of "slow" type 1 fibers) from the ex ternal TA (in which "fast" type 2 fibers predominated, especially in its ro stral part). Reconstruction of serial frontal sections of the TA allowed th e stereoscopic study of each division. The existence of a rudimentary laryn geal ventricle separating the true and false vocal folds in cats was demons trated anatomically and histologically, and its relationships to each divis ion of the TA were established. Our results suggest that the vocalis, fitte d for enduring activities, is suited for voice control. The fast, rostral p art of the external TA seems suited to laryngeal sphincteric demands, while its caudal counterpart may act in both functions. The anatomic individuali zation of the divisions of the TA may suggest that they play distinct physi ological roles and may imply that they should not be considered a single fu nctional unit.