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 from respiratory muscle nerves of the thorax and abdomen. In order to better understand the functional significance of vestibulo-respiratory reflexes, we investigated the extent to which such responses are also present on muscle nerves of the upper airway. Experiments were conducted on adult cats that were decerebrated, paralyzed, and artificially ventilated. Electrical stimulation of the vestibular nerve using short trains of current pulses evoked reflex responses on the following nerves: recurrent laryngeal, superior laryngeal, pharyngeal branch of the vagus, glossopharyngeal, and hypoglossal. The responses were bilateral and occurred on average within about 15 ms after stimulus onset. The medial and inferior vestibular nuclei were shown to be essential for the reflex, since the responses were abolished by injections of the neurotoxin kainic acid into these nuclei. The widespread presence of vestibular-evoked responses recorded from respiratory muscle nerves of the upper airway. as well as from those of the thorax and abdomen, suggests that one function of vestibulo-respiratory reflexes is to provide adjustments in breathing and airway patency during movements and changes in posture.