title: Respiratory-related recruitment of the masseter: response to hypercapnia and loading.
abstract: To test the hypothesis that a muscle that closes the jaw, the masseter, can be recruited by ventilatory stimuli, we studied the electromyographic activation of the masseter and genioglossus in seven normal awake males who were exposed in random order to progressive hyperoxic hypercapnia, inspiratory threshold loading (-40 cmH2O), and combined hypercapnia and loading. With hypercapnia, the masseter was generally recruited after the genioglossus had been activated. Once recruited, activation of both muscles increased linearly with increasing CO2. Combined hypercapnia and loading produced more activation than either stimulus alone. These data indicate that the masseter is activated by ventilatory stimuli that activate the genioglossus. Earlier recruitment of the genioglossus suggests that activation of the masseter serves to stabilize the mandible and allow the genioglossus to function as a more efficient dilator of the upper airway.
authors.affiliation: Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville 22908.
authors.forename: D E
authors.initials: DE
authors.lastname: Hollowell
authors.forename: P R
authors.initials: PR
authors.lastname: Bhandary
authors.forename: A W
authors.initials: AW
authors.lastname: Funsten
authors.forename: P M
authors.initials: PM
authors.lastname: Suratt
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D008406:Masseter Muscle / Q000294:innervation / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D013314:Stress, Mechanical