posterior cricoarytenoid

ANATOMY: Origin – posterior surface of the cricoid lamina. Insertion – muscular process of the arytenoid cartilage. Action – pulls the muscular process posteromedially, rotating the arytenoid externally so the vocal processes swing laterally, ABDUCTING the vocal folds and widening the rima glottidis (inspiration, quiet breathing). It is the sole abductor of the vocal cords. Innervation – recurrent (inferior) laryngeal nerve (CN X; derived from the 6th pharyngeal arch). Blood supply – inferior laryngeal artery (from inferior thyroid artery) and the superior laryngeal artery.

ANTAGONISTS/OTHER INTRINSIC MUSCLES: Lateral cricoarytenoid (adducts, closes glottis), transverse and oblique arytenoids (adduct, close the posterior glottis/intercartilaginous portion), thyroarytenoid (relaxes cords, shortens), vocalis (fine tuning), cricothyroid (tenses/lengthens the cords; the ONLY intrinsic laryngeal muscle innervated by the external branch of the superior laryngeal nerve). All other intrinsic muscles are supplied by the recurrent laryngeal nerve.

CLINICAL SIGNIFICANCE: - Unilateral recurrent laryngeal nerve injury (e.g., thyroidectomy, aortic arch aneurysm, left-sided lung/mediastinal tumors such as Pancoast or lymphadenopathy, left atrial enlargement/Ortner syndrome, cardiovocal): the affected cord lies in paramedian position (PCA paralysis and unopposed cricothyroid action) -> hoarseness, breathy voice. - Bilateral recurrent laryngeal nerve injury (e.g., total thyroidectomy): both cords are paramedian/adducted -> inspiratory stridor, dyspnea, acute airway obstruction; may require tracheostomy. - Semon's law: in progressive recurrent laryngeal nerve lesions, abductors (PCA) fail first, followed by adductors – so early lesions cause cord adduction (airway risk), later lesions cause cadaveric position. - Recurrent laryngeal nerve laterality: the right RLN loops around the right subclavian artery; the left loops around the aortic arch (ligamentum arteriosum), making the left more vulnerable to thoracic pathology. During thyroidectomy, the RLN runs in the tracheoesophageal groove near the inferior thyroid artery ("water under the bridge" – the nerve is deep to the artery... classically the ureter/uterine artery mnemonic; for the thyroid, the RLN is at risk during ligation of the inferior thyroid artery). - Superior laryngeal nerve (external branch) injury affects cricothyroid -> loss of high pitch (singers' complaint), not airway compromise. - Succinylcholine/neuromuscular blockade and laryngospasm: the PCA is relatively sensitive to fatigue; in laryngospasm the adductors overpower it. - Vocal cord paralysis workup: laryngoscopy, then imaging of the course of the RLN (neck to mediastinum; CT chest/neck).

HIGH-YIELD PEARLS: Only abductor of cords; RLN innervation; bilateral injury -> stridor; remember cricothyroid is the sole exception to RLN supply for intrinsic muscles; sensory supply above cords is internal branch of the superior laryngeal nerve, and below cords is the RLN.