Effect of superior laryngeal nerve transection on pharyngeal muscle contraction timing and sequence of activity during eating and stimulation of the nucleus solitarius in dogs.

The effect of unilateral or bilateral transection of the superior laryngeal nerve on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in 10 dogs during eating and during unilateral electrical stimulation of the solitary nucleus. In all groups of dogs, after unilateral or bilateral transection, there were some swallowing actions in which the sequence of activity in the pharyngeal muscles was disturbed during eating and during stimulation of the solitary nucleus. In the dogs in which the transection was unilateral, this fraction was 18% in the ipsilateral muscles during eating and 7% in the contralateral muscles. After bilateral transection it was 8% in the left muscles and 16% in the right muscles. The fractions were not significantly different when swallowing was evoked by stimulation of the solitary nucleus. Swallowing actions having a normal sequence of activity in these dogs were compared with those in a group of eight dogs in which the superior laryngeal nerves were intact. Contraction timing was not significantly different during eating, but during stimulation of the solitary nucleus the timing was significantly shorter than in the dogs with intact nerves. It was concluded that superior laryngeal nerve transection modulates the central pattern generator for pharyngeal swallowing in dogs.