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Muscle Spindles are Concentrated in the Superior Vocalis Subcompartment of the Human Thyroarytenoid Muscle

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Ira SandersGrabscheid Voice Center, Department of Otolaryngology, Mount Sinai Medical Center, New York, New York, U.S.A.
Yingshi HanGrabscheid Voice Center, Department of Otolaryngology, Mount Sinai Medical Center, New York, New York, U.S.A.
Jun WangGrabscheid Voice Center, Department of Otolaryngology, Mount Sinai Medical Center, New York, New York, U.S.A.
Hugh BillerGrabscheid Voice Center, Department of Otolaryngology, Mount Sinai Medical Center, New York, New York, U.S.A.

Summary: It is hypothesized that different parts of the thyroarytenoid muscle (TA) are functionally specialized. Specifically, the TA is divided into a lateral muscularis compartment and a medial vocalis compartment. This study examined the distribution of muscle spindles throughout the human TA as an indicator of these functional differences. Histological cross-sections from the anterior, middle, and posterior regions of five human membranous vocal folds were examined for the number and location of muscle spindles. There was an average of 6.1 muscle spindles in sections from each region with no significant variation between the different regions (p

The results of this study demonstrate that the majority of TA muscle spindles are concentrated in its superior medial quadrant, an area we have termed the superior vocalis subcompartment (SC). This finding suggests that the superior vocalis SC is functionally distinct from the remainder of the TA. It is hypothesized that tension in the superior vocalis SC can be controlled independently from the remainder of the TA, and this capability is used to effect the biomechanics of vocal fold vibration during phonation. Key Words: Larynx--Voice--Thyroarytenoid muscle--Vocalis--Vocal fold--Muscle spindle.

The principle component of the vocal fold is the thyroarytenoid muscle (TA). TA activity during phonation can potentially affect the biomechanics of the vibrating vocal fold in various ways. For example, by shortening the vocal fold, it can relax the vocal fold cover and lower pitch (1). Paradoxically, contraction of parts of the...