Craniofacial Muscles

146 L.A. Vinney and N.P. Connor
Fig. 9.2 Endoscopic images shown with simultaneous EMG information from one individual’s
10 mL bolus swallow. A arytenoid adduction begins; B total arytenoid adduction; C open glottis
and forward tilt of arytenoid cartilages; D inversion of epiglottis just before whiteout; E just after
whiteout (open glottis); SM submental muscle; CP cricopharyngeus muscle; LP longitudinal
pharyngeal muscle; GG genioglossus muscle; SPC superior pharyngeal constrictor muscle; TA
thyroarytenoid muscle; PCA posterior cricoarytenoid muscle. Used with permission by the fi rst
author and publisher from Van Daele et al. ( 2005 )
muscle contractions depending on whether inspiration or expiration is occurring
(for review, see Woodson 1999 ) . For example, during wakefulness, the PCA is phasically
active on inspiration and tonically active on expiration (Kuna et al. 1990 ) .
The IA and TA muscles, on the other hand, are typically phasically active during
expiration and tonically active during inspiration (Kuna et al. 1988, 1991 ; Kuna and
Insalaco 1990 ) . Thus, vocal fold position during quiet breathing in awake individuals
results from the interaction of muscle antagonists (Kuna et al. 1990 ) .
The activity of the TA muscle during wakefulness is particularly unique.
Speci fi cally, the TA appears to promote a degree of vocal fold adduction during
expiration and its action has been linked to resistance at the lungs and below the
epiglottis during expiration (Kuna et al. 1988 ) . When expiration begins, TA activity
typically increases and then either levels off or gradually increases or decreases
depending on expiratory length. These changes in activation patterns are associated
with amount of expiratory air fl ow and time of expiration. Longer expirations and
less air fl ow occur at the end of the expiratory cycle when TA activations are high
(Kuna et al. 1988 ) . The TA actively in fl uences an increase in expiratory durations
because it increases resistance at the glottis. This action can be thought of as a
“laryngeal braking mechanism” (Kuna et al. 1988 ) .
Intrinsic muscles of the larynx are active during swallowing. As shown in
Fig. 9.2 , combined EMG and endoscopy recordings have indicated that laryngeal