Laryngeal Electromyography: Basic Concepts and Clinical Uses

Laryngeal electromyography (LEMG) is a procedure that evaluates the integrity of the muscular and nervous systems of the larynx. This test is performed on patients who have evidence of a movement disorder of the vocal folds. The purpose of the LEMG is to help the physician diagnose and differentiate the causes of these movement disorders. There are several different types of problems that can result in abnormal motions of the vocal folds. These can be classified as disorders in movements of the joints that connect the cartilages of the larynx, primary problems within the muscles themselves, or problems in the nerves that supply the muscles of the larynx. Understanding the exact mechanism of the problem is important in helping the physician understand how to treat the patient's voice problems best and in helping speech-language pathologists and singing teachers select the best exercises to help rehabilitate the voice. When a person makes a decision to vocalize, the brain initiates the phonation by sending an electrical signal to the brainstem, which then transfers the impulse through the recurrent and superior laryngeal nerves. The superior and recurrent laryngeal nerves are paired, one of each supplying the muscles of the left and right vocal folds. The superior laryngeal nerve innervates the cricothyroid muscle, which is the muscle that lengthens the vocal folds to in-crease pitch. The recurrent laryngeal nerve supplies the thyroarytenoid, interarytenoid, lateral cricoarytenoid, and posterior cricoarytenoid muscles. The thyroarytenoid, interarytenoid, and lateral cricoarytenoid muscles help with vocal fold adduction (closing the vocal folds) during phonation. The posterior cricoarytenoid muscles abduct (open) the vocal folds. As the electrical impulse reaches the end of the nerve, it signals the release of a substance called a neurotransmitter from the tip of the nerve. In the larynx, the predominant neurotransmitter is a chemical called acetylcholine. As this neurotransmitter is released from the end of the nerve, it then binds to its receptor on the muscle. The region that consists of the nerve ending, the muscle receptor for acetylcholine, and the space between the nerve ending and the muscle receptor is of-ten referred to as the neuromuscular junction. When this neurotransmitter binds to its receptor on the musθουρναλ οφ Σινγινγ, θανυαρψ/Φεβρυαρψ 2002