Changing in pitch of the sound is produced by which muscle –
**Core Concept**
The pitch of sound produced by the voice box (larynx) is determined by the tension and length of the vocal cords. This relationship is described by the **vocal cord length-tension relationship**, where changes in pitch are directly related to changes in the tension of the vocal cords. The muscles responsible for altering this tension are key to modulating the pitch of sound produced.
**Why the Correct Answer is Right**
The correct answer is the posterior cricoarytenoid muscle, which is responsible for **abducting the vocal cords**, thereby increasing the distance between them and reducing tension. This results in a decrease in pitch. In contrast, adduction of the vocal cords, achieved by muscles such as the thyroarytenoid and cricothyroid, increases tension and results in a higher pitch. The posterior cricoarytenoid muscle is the only muscle that can move the vocal cords apart, making it the primary muscle responsible for changing the pitch of sound produced.
**Why Each Wrong Option is Incorrect**
* **Option A:** The vocalis muscle is involved in adjusting the length of the vocal cords but does not primarily affect pitch.
* **Option B:** The cricothyroid muscle increases tension on the vocal cords, resulting in a higher pitch, not a lower pitch.
* **Option D:** The arytenoid muscle is involved in adduction and abduction of the aryepiglottic fold, but not directly in modulating pitch.
**Clinical Pearl / High-Yield Fact**
When assessing a patient with hoarseness or voice changes, remember that a **shortened or paralyzed vocal cord** can result in a higher pitch due to increased tension, and a **lengthened or paralyzed vocal cord** can result in a lower pitch due to decreased tension.
**Correct Answer:** C.