The superior laryngeal nerve.
Injury to the internal (sensory) branch of the superior laryngeal nerve during thyroidectomy is unlikely. Signs of injury are loss of sensation in the upper larynx, resulting in choking and aspiration of swallowed fluids. Injury to the external (motor) branch of the superior laryngeal nerve produces no problem of respiration, but may result in changes in the quality of the voice or even voicelessness. Injury to the external branch can be avoided if the anatomical variations are kept in mind during ligation of upper pole vessels.
D006801:Humans; D061224:Laryngeal Nerve Injuries; D007823:Laryngeal Nerves / Q000033:anatomy & histology; D013959:Thyroid Diseases / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects