Upper airway motor outputs during vomiting versus swallowing in the decerebrate cat

Swallowing and vomiting are antagonistic motor acts; nevertheless, vomiting can be immediately followed by swallowing. The purpose of this study was to clarify the interrelationship between these two behaviors, particularly in regard to comparing the upper airway motor patterns at the end of the expulsion phase with those during subsequent swallowing. Experiments were conducted using both paralyzed and non-paralyzed decerebrate cats, in which recordings were obtained either from upper airway muscles, the diaphragm and abdominal muscles or from the nerves that innervate those muscles. The activity patterns of most nerves recorded in paralyzed animals were consistent with the behavior recorded in non-paralyzed animals from the muscles innervated by those nerves, with the exception of the cricothyroid and stylopharyngeus muscles. Vomiting can be divided into a series of retches followed by expulsion, which itself can be further subdivided into three phases. The final stage of expulsion, characterized by burst-like exaggerated activity of the laryngeal elevator thyrohyoid and the pharyngeal constrictors, proved to be different from pharyngeal swallowing, as judged from differences in the spatio-temporal patterns of the upper airway motor outputs. However, post-vomiting swallowing activity was still observed even after total deafferentation of the laryngeal and pharyngeal areas in paralyzed animals. It is therefore likely that the central processes for vomiting and swallowing closely relate in generating these two behaviors.