posterior crico-arytenoid
The posterior cricoarytenoid muscles are extremely small, paired muscles that extend from the posterior cricoid cartilage to the arytenoid cartilages in the larynx. By rotating the arytenoid cartilages laterally, these muscles abduct the vocal cords and thereby open the rima glottidis. Their action opposes the lateral cricoarytenoid muscles. The posterior cricoarytenoid muscles receive innervation from the recurrent laryngeal branch of the vagus nerve (CN X). Paralysis of the posterior cricoarytenoid muscles may lead to asphyxiation as they are the only laryngeal muscles to open the true vocal folds, allowing inspiration and expiration.