Explain Myoelastic Aerodynamic Theory

Myoelastic-aerodynamic theory is the term used to describe the way that the vocal folds vibrate. The theory consists of an interaction of muscle forces (myo), elastic recoil forces (elastic), and aerodynamic forces. I will now describe the myoelastic-aerodynamic theory using the following diagram. Diagram A starts on the exhalation phase and the vocal folds are in phonatory position. The vocal folds are contracted by the Interarytenoids and the Lateral cricoid arytenoids. These muscles (IA and LCA) put the vocal folds in the phonotory position to initiate the vibratory cycle. Medial compression is the force exerted by the IA and LCA. The LCA and IA remain contracted throughout phonation when in the phonatory position. Diagram B and C show the …show more content…
As air moves through the glottis and is exerting pressure on the vocal folds. The IA and LCA are still trying to hold the vocal folds at midline. The subglottal pressure builds up and pushes up the inferior edges of the vocal folds and pushes the inferior portions apart. This occurs when the subglottal pressure overcomes medial compression. The minimum amount of subglottal pressure need to separate the vocal folds is the phonation threshold pressure (PTP). The typically minimum phonation threshold pressure need to set the vocal folds into vibration is 3 to 8 cm H20. Diagram D shows the glottis opening. Vocal folds are pushed apart and the glottis space widens and this increases air volume and speed. Diagram E shows the open glottis. Elastic recoil and negative pressure cause the vocal folds to close. The elastic recoil force the vocal fold lower margins to close and decreasing the space between the folds. This decrease in space makes the air flowing through the glottis speed up. The increase in speed results in a decrease in pressure. The decrease in pressure causes a suction effect that makes the vocal folds come …show more content…
This occurs because of the cellular makeup of the vocal folds. The superficial and upper layers are more pliable. Vibrations occur when air flows through the trachea and larynx. The vibrations consist of lateral and medial movements that produce the mucosal wave as the vibrations travel from lower to upper vocal folds. There is a slight time lag between the approximation and separation of lower and upper edges of vocal folds. This is called the vertical phase difference. The vocal folds close the glottis horizontally from anterior to posterior and posterior to anterior (similar to a zipper). The glottis closes in the opposite direction from anterior to posterior thus creating a time lag called the longitudinal phase difference. These movements contribute to that mucosal wave motion. Convergent and Divergent are terms used to describe the glottis shape during vibration. Convergent shape is used to describe when the vocal folds separate farther apart at the bottom margins and less at the superior margin. This shape results in the glottis opening from the positive pressure within the glottis. Divergent shape will be discussed during glottal

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