Vocal Cord Paralysis: Pathophysiology, Etiologies, and Evaluation

studies suggesting additional motor contributions from the internal branch of the SLN. 6The LCA muscle is a strong adductor of the vocal folds.All laryngeal functions requiring glottic closure such as phonation, coughing, straining, and Valsalva's maneuver require a strong contraction of the LCA muscle.Likewise, the PCA muscle is the primary abductor of the vocal folds, with inspiratory vocal fold abduction being the most important function of this muscle. 7The IA muscle is comprised of three muscles, the transverse arytenoid muscle and two oblique arytenoid muscles. 1 It is theorized that the IA muscle may assist in vocal fold adduction, aiding to close the posterior glottis, however the function is not completely understood. 5,8 Superior Laryngeal NerveThe SLN branches from the vagus nerve just below the level of the jugular foramen, inferior to the nodose ganglion, which contains the sensory cell bodies of the SLN. 1 The SLN then takes a direct course to the larynx, traveling medial to the carotid artery and divides into two branches at the level of the hyoid bone.The internal branch of the SLN penetrates the thyrohyoid membrane and is sensory to the supraglottic larynx as well as potentially contributing motor fibers to the IA muscle. 6The external branch of the SLN provides motor innervation of the CT muscle.The CT muscle is primarily