The vocalis is the familiar name for the thyroarytenoid muscle, a muscle of the larynx, or voice box, in the throat. Shaped like a tiny strap, it is a paired muscle that spans the larynx horizontally from front to back like a pair of parallel strings crossing the sound hole on a guitar. The vocalis is found immediately to either side of and running parallel to two more strings of tissue: the vocal cords. More appropriately known as the vocal folds, these vibrating lengths of membrane are adducted, or drawn together, by the vocalis to assist the other laryngeal muscles in speech production.
Situated within the portion of the larynx that is enveloped by the thyroid cartilage — better known as the Adam’s apple — the vocalis originates on its front end on the thyroid cartilage. This cartilage is shaped much like the jawbone above it, only on a smaller scale. It wraps the front and sides of the larynx, forming a sort of protective wall. The tiny vocalis muscle attaches to either angle of the thyroid cartilage alongside the vocal folds approximately midway down the larynx.
From here, the vocalis runs backward and ever so slightly outward across the larynx to attach to the front of a paired horned-shaped cartilage known as the arytenoid cartilage. The vocal folds attach here as well. When the vocalis muscle contracts, like all skeletal muscle it shortens, pulling anteriorly or forward on the arytenoid cartilage and allowing the vocal folds to loosen. Similarly, some of the lower fibers of this muscle are flush with those of the vocal folds and draw them downward and together, resulting in an action known as adduction of the vocal folds. These also contribute to the thickness of the vocal folds.
The ability of the vocalis to adduct the vocal folds as well as alter their tightness and thickness means that this muscle’s action alters the pitch and tone of speech. Tests of activity in the laryngeal muscles during particular speech patterns have shown that, for instance, the vocalis is active when a person’s voice goes up at the end of a sentence as it does upon asking a question. It alters the pitch of speech by changing the tension of the vocal folds, causing them to slacken as the muscle pulls forward on the arytenoid cartilage. This in turn affects the rate at which the vocal folds vibrate as air is pushed through on its way from the lungs toward the mouth, and it is the speed of vocal fold vibration that determines the pitch of one’s voice.