Which muscle is responsible for abduction of vocal cord, in the given diagram

**Core Concept**
The question is testing the student's knowledge of laryngeal muscles and their functions. The correct answer is related to the muscles of the larynx, specifically those involved in vocal cord movement. The correct muscle is responsible for the abduction of the vocal cord, which is a crucial function in vocal cord movement.

**Why the Correct Answer is Right**
The muscle responsible for the abduction of the vocal cord is the posterior cricoarytenoid muscle. This muscle is innervated by the recurrent laryngeal nerve, a branch of the vagus nerve. When the posterior cricoarytenoid muscle contracts, it rotates the arytenoid cartilage, resulting in the abduction of the vocal cord. This movement is essential for breathing and for the production of speech sounds.

**Why Each Wrong Option is Incorrect**
* **Option A:** The thyroarytenoid muscle is responsible for vocal cord addiction, not abduction. It is also innervated by the recurrent laryngeal nerve.
* **Option B:** The cricothyroid muscle is responsible for tensing the vocal cords, which is essential for pitch changes in speech. However, it does not abduct the vocal cords.
* **Option C:** The arytenoid muscle is not a specific muscle, but rather a cartilaginous structure that is moved by the posterior cricoarytenoid muscle.

**Clinical Pearl / High-Yield Fact**
The posterior cricoarytenoid muscle is the only muscle that abducts the vocal cord, making it essential for breathing. This muscle is often compromised in patients with vocal cord paralysis, leading to breathing difficulties.

**Correct Answer:** C.