Adaptation in the function of pharyngeal constrictor muscles.

The palatopharyngeus and pharyngeal constrictor muscles were studied by electromyography (EMG) and by direct observation with a flexible fiberoptic scope in the anesthetized as well as in the alert rhesus monkey. The muscles were monitored to determine the change in their discharge with nasal obstruction, head posture, head extension, and swallowing. The results indicated that certain regions of the middle and inferior pharyngeal constrictors never discharged during deglutition. Extending the head could induce a tonic discharge in fibers of the middle pharyngeal constrictor for the duration of head extension. Placement of water in the hypopharynx not only induced a sustained laryngospasm but also a tonic discharge in the select fibers of the superior and middle pharyngeal constrictors. Changing from a supine to an upright posture, or obstructing the nasal cavity, could induce a rhythmic discharge. These studies indicate that there are functional components of fibers within each of the anatomically recognized pharyngeal constrictors.