Safety muscle of larynx is:
**Core Concept**
The safety muscle of the larynx is a crucial anatomical structure that prevents aspiration of food, liquids, or other foreign materials into the airway. It is a vital component of the laryngeal mechanism that maintains airway patency and protects against potential asphyxiation.
**Why the Correct Answer is Right**
The correct answer is the cricothyroid muscle. The cricothyroid muscle is the only intrinsic muscle of the larynx that is innervated by the external branch of the superior laryngeal nerve. This unique innervation allows it to function as the "safety muscle" of the larynx, as it is the last muscle to be paralyzed by a superior laryngeal nerve injury. The cricothyroid muscle's primary function is to tighten the vocal cords, thereby preventing aspiration of foreign materials into the airway.
**Why Each Wrong Option is Incorrect**
* **Option A:** The thyroarytenoid muscle is not considered the safety muscle of the larynx, as it primarily functions to relax the vocal cords, not tighten them.
* **Option B:** The posterior cricoarytenoid muscle is the primary abductor of the vocal cords, but it is not considered the safety muscle of the larynx.
* **Option C:** The arytenoid muscle is not a distinct muscle, but rather a pair of cartilages that form the posterior aspect of the larynx.
**Clinical Pearl / High-Yield Fact**
In a patient with a suspected superior laryngeal nerve injury, the presence of normal cricothyroid muscle function can be a critical indicator of airway patency and guide management decisions.
**Correct Answer: C. Cricothyroid muscle**