Injury to superior laryngeal nerve causes

Paralysis of the superior laryngeal nerve causes paralysis of cricothyroid muscle and ipsilateral anaesthesia of the larynx above the vocal cord. Paralysis of cricothyroid can also occur when the external laryngeal nerve is involved in thyroid surgery, tumours, neuritis or diphtheria. Voice is weak and pitch cannot be raised with decreased ability to sing. Flapping of the paralyzed cord. As the tension of the cord is lost, it sags down during inspiration and bulges up during expiration. Ref: PL Dhingra Textbook of Ear, Nose and Throat, Edition 7, page - 339