Abductor of the vocal cord is: (Repeat)
**Core Concept**
The question is testing the student's knowledge of the muscles involved in the movement of the vocal cords. The abductor muscles are responsible for separating the vocal cords, whereas the adductor muscles bring them together. This movement is essential for various functions, including speech and breathing.
**Why the Correct Answer is Right**
The correct answer is the posterior cricoarytenoid muscle, which is the only abductor of the vocal cords. This muscle is innervated by the recurrent laryngeal nerve and is responsible for rotating the arytenoid cartilages, thereby separating the vocal cords. This movement is crucial for opening the glottis during inspiration.
**Why Each Wrong Option is Incorrect**
* **Option A:** The thyroarytenoid muscle is an adductor of the vocal cords, not an abductor. It is responsible for relaxing the vocalis muscle, which helps to shorten the vocal cord.
* **Option B:** The cricothyroid muscle is an adductor of the vocal cords, as it lengthens and tenses the vocal cord. It is also responsible for increasing the pitch of the voice.
* **Option C:** The lateral cricoarytenoid muscle is an adductor of the vocal cords, as it rotates the arytenoid cartilages to bring the vocal cords together.
**Clinical Pearl / High-Yield Fact**
The posterior cricoarytenoid muscle is the only abductor of the vocal cords, and its paralysis can lead to bilateral vocal cord immobility, which can cause inspiratory stridor.
**Correct Answer:** D. Posterior cricoarytenoid muscle.