What is the effect of the thyroarytenoid muscle on the vocal folds?

The thyroarytenoid muscle plays a significant role in the adjustment of the vocal folds during phonation. When this muscle contracts, it shortens and relaxes the vocal folds, which causes a decrease in the distance between the thyroid and arytenoid cartilages. This action is critical for modulating the tension and mass of the vocal folds, directly influencing pitch and vocal quality. By decreasing this distance, the thyroarytenoid muscle effectively contributes to producing lower frequencies in sound, as the folds become thicker and less tense.

The other choices do not accurately reflect the primary function of the thyroarytenoid muscle. For instance, increasing vocal pitch is generally a result of elongation and tightening of the vocal folds, which is more associated with the cricothyroid muscle rather than the thyroarytenoid. Abduction of the arytenoids is accomplished by the posterior cricoarytenoid muscles, while breath support involves a more complex interaction of multiple muscle groups, not solely attributed to the thyroarytenoid muscle itself. Thus, the correct choice emphasizes the primary action of the thyroarytenoid in adjusting the position and tension of the vocal folds.