Activity of lingual, laryngeal and oesophageal receptors in conscious sheep.

Vagal afferent impulse traffic has been studied in conscious sheep by electromyographic recording from the motor units of the sterno-cleido-mastoid (s.c.m.) muscle reinnervated by sensory vagal axons. Units which responded during movements of the tongue and during the pharyngolaryngeal and oesophageal stages of swallowing were chosen for this study. Lingual units showed a phasic discharge bearing a temporal relation to movements of the tongue during licking of the lips or chewing of a bolus before swallowing. Laryngeal units had no spontaneous activity. A discharge occurred with the ascending movement of the larynx during swallowing. Oesophageal units did not exhibit any tonic activity. They fired only at the time of primary or secondary oesophageal peristalsis. The oesophageal units showed a bimodal distribution. The oesophageal receptors are more concentrated at the beginning and the end of the thoracic oesophagus. During primary peristalsis, the afferent discharge was reinforced in only 57% of the cases when sheep swallowed a bolus (pellets or inflated balloons). When the discharge was reinforced, its increase ceased as volumes of the bolus were increased from 20 to 40 ml. During local oesophageal contractions, the afferent discharge was only present when the inflated balloon was located at the site of the receptor. It was enhanced at the time the primary peristaltic wave passed over the balloon. Inflation of a second balloon cranially in the oesophagus led to abolition of the activity of the unit at the caudal site though the distension there was maintained.