Vocal fold movements are a result of the coordinated contraction of various muscles. These muscles are controlled by the brain through a specific set of nerves. The nerves that receive these signals are the:
Superior laryngeal nerve (SLN), which carries signals to the cricothyroid muscle, located between the cricoid and thyroid cartilages. Since the cricothyroid muscle adjusts the tension of the vocal fold for high notes during singing, SLN paresis and paralysis result in abnormalities in voice pitch and the inability to sing with smooth change to each higher note. Sometimes, patients with SLN paresis/paralysis may have a normal speaking voice but an abnormal singing voice.
The recurrent laryngeal nerve (RLN) carries signals to different voice box muscles responsible for opening vocal folds (as in breathing, coughing), closing vocal folds for vocal fold vibration during voice use, and closing vocal folds during swallowing. The recurrent laryngeal nerve goes into the chest cavity and curves back into the neck until it reaches the larynx. Because the nerve is relatively long and takes a "detour" to the voice box, it is at greater risk for injury from quite different causes – such as infections and tumors of the brain, neck, chest, or voice box; as well as complications during surgical procedures in the head, neck, or chest regions – that directly injure, stretch, or compress the nerve. Consequently, the recurrent laryngeal nerve is involved in majority of cases of vocal fold paresis or paralysis.