superior laryngeal nerve
Summary
The superior laryngeal nerve is a branch of the vagus nerve (CN X) that divides into internal and external branches. The internal branch provides sensory innervation to the supraglottis, while the external branch (motor) innervates the cricothyroid muscle, which is crucial for vocal pitch control.
Detail
The superior laryngeal nerve originates from the inferior ganglion of the vagus nerve and descends alongside the internal carotid artery. It bifurcates into two functionally distinct branches: (1) The internal branch penetrates the thyrohyoid membrane to provide sensory innervation to the epiglottis, aryepiglottic folds, and supraglottic larynx above the vocal cords, and also carries parasympathetic fibers to laryngeal glands. (2) The external branch descends along the lateral aspect of the thyroid cartilage to innervate the cricothyroid muscle, the only intrinsic laryngeal muscle not supplied by the recurrent laryngeal nerve. The cricothyroid muscle elongates and tenses the vocal cords, making it essential for pitch elevation and voice quality. Injury to the external branch (often during thyroid surgery) results in inability to tense vocal cords, causing voice weakness, inability to reach high pitches, and vocal fatigue. This nerve is clinically significant because it can be damaged during anterior neck procedures, particularly thyroidectomy, leading to characteristic voice changes that affect professional singers and speakers.
Sources
- Gray's Anatomy
- Netter's Atlas of Human Anatomy
- First Aid for the USMLE Step 1
- Moore's Clinically Oriented Anatomy
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