## **Core Concept**
The sensory supply of the larynx is divided into two parts: above and below the vocal cords. The **recurrent laryngeal nerve**, a branch of the **vagus nerve (cranial nerve X)**, provides sensory innervation to the larynx below the vocal cords.

## **Why the Correct Answer is Right**
The recurrent laryngeal nerve is responsible for the sensory supply of the larynx below the vocal cords. This part of the larynx includes the **infraglottic cavity** and the **subglottis**. The recurrent laryngeal nerve arises from the vagus nerve and loops around the subclavian artery on the right and the ductus arteriosus (ligamentum arteriosum) on the left, before ascending back to the larynx. This nerve provides crucial sensory information from the area below the vocal cords.

## **Why Each Wrong Option is Incorrect**
* **Option A:** The **internal laryngeal nerve**, another branch of the **superior laryngeal nerve** (also originating from the vagus nerve), provides sensory innervation to the part of the larynx **above** the vocal cords, including the **epiglottis**, **aryepiglottic folds**, and the **supraglottic area**. Therefore, it does not supply the area below the vocal cords.
* **Option B:** The **external laryngeal nerve**, also a branch of the **superior laryngeal nerve**, primarily provides **motor innervation** to the **cricothyroid muscle**. It does not contribute to the sensory supply of the larynx.
* **Option D:** The **superior laryngeal nerve** itself has two branches: the internal and external laryngeal nerves. While it does provide sensory innervation to the larynx, it is limited to the area **above** the vocal cords.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the **recurrent laryngeal nerve** can be damaged during **thyroid surgery** or in conditions like **thoracic surgery** or **Pancoast tumors**, leading to vocal cord paralysis and potentially life-threatening airway compromise. The sensory supply below the vocal cords is critical for the cough reflex and protection of the airway.

## **Correct Answer:** C. Recurrent laryngeal nerve.