Which nerve doesn’t supply the laryngeal muscles?
**Core Concept**
The laryngeal muscles are responsible for controlling the movement of the vocal cords and maintaining airway patency. The cranial nerves that innervate these muscles originate from the brainstem and play a crucial role in regulating vocal cord function and respiration.
**Why the Correct Answer is Right**
The recurrent laryngeal nerve (RLN) and the superior laryngeal nerve (SLN) are the primary nerves that supply the intrinsic muscles of the larynx, including the cricothyroid, thyroarytenoid, and arytenoid muscles. The RLN originates from the vagus nerve (CN X) and courses through the neck, eventually joining the vagus nerve again before innervating the laryngeal muscles. The SLN also arises from the vagus nerve and provides sensory innervation to the larynx. In contrast, the vagus nerve itself does not directly innervate the laryngeal muscles, as this function is mediated by its branches, the SLN and RLN.
**Why Each Wrong Option is Incorrect**
**Option A:** The **trigeminal nerve** (CN V) is responsible for facial sensation and motor function, including eye movements, but it does not innervate the laryngeal muscles.
**Option B:** The **facial nerve** (CN VII) controls facial expressions, taste, and some motor functions, but it does not innervate the laryngeal muscles.
**Option C:** The **vagus nerve** (CN X) is the parent nerve of the SLN and RLN, but it does not directly innervate the laryngeal muscles.
**Clinical Pearl / High-Yield Fact**
The vagus nerve is often referred to as the "tenth cranial nerve," but it is not directly responsible for innervating the laryngeal muscles. Instead, its branches, the SLN and RLN, perform this function.
**Correct Answer:** B. The facial nerve (CN VII).