Injury of which of these nerve cause vocal cord paralysis?
**Core Concept**
The question is testing the knowledge of the nerves responsible for the motor innervation of the larynx, specifically the vocal cords. The recurrent laryngeal nerve (RLN) and the superior laryngeal nerve (SLN) are the two branches of the vagus nerve that provide motor innervation to the laryngeal muscles.
**Why the Correct Answer is Right**
The recurrent laryngeal nerve is responsible for the motor innervation of all the intrinsic muscles of the larynx except for the cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve. The RLN provides motor innervation to the posterior cricoarytenoid, lateral cricoarytenoid, arytenoid, and the thyroarytenoid muscles, which are responsible for the opening and closing of the glottis and the tension of the vocal cords. Injury to the RLN can result in vocal cord paralysis, leading to hoarseness of voice, breathlessness, and difficulty swallowing.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is the correct answer, so we will skip it.
* **Option B:** The hypoglossal nerve (CN XII) provides motor innervation to the muscles of the tongue, not the larynx.
* **Option C:** The facial nerve (CN VII) provides motor innervation to the muscles of facial expression, not the larynx.
* **Option D:** The glossopharyngeal nerve (CN IX) provides sensory innervation to the pharynx, not the motor innervation of the larynx.
**Clinical Pearl / High-Yield Fact**
The recurrent laryngeal nerve is particularly vulnerable to injury during thyroid and parathyroid surgery, and identification of the nerve is crucial during these procedures to prevent vocal cord paralysis.
**Correct Answer: A. The recurrent laryngeal nerve.**