VESTIBULAR EFFECTS ON UPPER AIRWAY MUSCULATURE

The vestibular system produces a variety of compensatory responses to accelerations of the head, which include reflex responses recorded fro m respiratory muscle nerves of the thorax and abdomen. In order to bet ter understand the functional significance of vestibulo-respiratory re flexes, we investigated the extent to which such responses are also pr esent on muscle nerves of the upper airway. Experiments were conducted on adult cats that were decerebrated, paralyzed, and artificially ven tilated. Electrical stimulation of the vestibular nerve using short tr ains of current pulses evoked reflex responses on the following nerves : recurrent laryngeal, superior laryngeal, pharyngeal branch of the va gus, glossopharyngeal, and hypoglossal. The responses were bilateral a nd occurred on average within about 15 ms after stimulus onset. The me dial and inferior vestibular nuclei wore shown to be essential for the reflex, since the responses were abolished by injections of the neuro toxin kainic acid into these nuclei. The widespread presence of vestib ular-evoked responses recorded from respiratory muscle nerves of the u pper airway, as well as from those of the thorax and abdomen, suggests that one function of vestibulo-respiratory reflexes is to provide adj ustments in breathing and airway patency during movements and changes in posture.