Which nerve innervates the cricothyroid muscle?

• A. Internal laryngeal nerve
• B. External laryngeal nerve
• C. Recurrent laryngeal nerve
• D. Superior laryngeal nerve

Answer: (B)

The cricothyroid muscle is the intrinsic laryngeal muscle that is uniquely innervated by the external branch of the superior laryngeal nerve. This branch provides motor fibers to the cricothyroid, which tilts the thyroid cartilage forward to tense the vocal cords and raise pitch. The internal laryngeal nerve carries sensory fibers to mucosa above the vocal cords, not motor to muscles. The recurrent laryngeal nerve supplies all the other intrinsic laryngeal muscles (like the posterior and lateral cricoarytenoids, and the thyroarytenoid/vocalis), so it does not innervate cricothyroid. Injury to the external branch can impair the ability to tense the vocal cords, leading to a weak or monotone voice.