Structure and Function of the Superior Laryngeal Nerve - The superior laryngeal nerve arises from the middle of the inferior ganglion of the vagus nerve. - It descends by the side of the pharynx deep to the internal carotid artery. - The nerve divides into two branches: the external laryngeal nerve and the internal laryngeal nerve. - The external laryngeal nerve descends on the larynx beneath the sternothyroid muscle to supply the cricothyroid muscle. - The internal laryngeal nerve descends to the thyrohyoid membrane and is distributed to the mucous membrane of the larynx. - The superior laryngeal nerve innervates the cricothyroid muscle.

Clinical Significance of Superior Laryngeal Nerve - Damage to the superior laryngeal nerve during thyroidectomy or cricothyrotomy can impair the ability to produce pitched sounds and cause voice fatigability. - Superior laryngeal nerve palsy can change the pitch of the voice and cause an inability to make explosive sounds. - Bilateral palsy of the superior laryngeal nerve presents as a tiring and hoarse voice. - Irritation of the internal laryngeal nerve can result in uncontrolled coughing and an increased risk of aspiration pneumonia. - An understanding of the anatomy and variations of the external laryngeal nerve is critical for preserving its integrity during surgery.

Additional Image - The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.

References - Grays Anatomy, 20th edition, page 912 (public domain text). - Lasts Anatomy, 12th edition, by Chummy S. Sinnatamby. - Pain Management Secrets, Third Edition, Chapter 19 - Glossopharyngeal and other Facial Neuralgias, by Robert A. Duarte and Charles E. Argoff. - World Journal of Surgery, 'Partial superior laryngeal nerve (SLN) lesions before and after thyroid surgery,' by S. Jansson et al. - Laryngoscope, 'External branch of the superior laryngeal nerve monitoring during thyroid and parathyroid surgery: International Neural Monitoring Study Group standards guideline statement,' by M. Barczyński et al.