An increase in the sensitivity of airway reflexes during induction of anaesthesia increases the likelihood of laryngeal spasm and coughing. Some early work identified two types of receptor in the larynx: one a slowly adapting receptor and the second a rapidly adapting receptor thought to be especially sensitive to chemical stimulants. Anaesthetic agents may sensitise the receptors, explaining why some inhaled and intravenous agents may easily precipitate laryngeal spasm. Prior to the administration of lidocaine airway irritation caused not only the cough reflex, but also other respiratory reflexes such as expiration, apnoea and spasmodic panting. It should be noted that the initial application of local anaesthetic agents to the airway may be associated with laryngospasm. It is now thought that the pharyngeal dilators, in addition to the diaphragm, comprise the efferent output of the respiratory centre. Tonic contraction is required to keep the tongue forward and maintain airway patency.