The vocal folds, being pliable and movable will begin to move toward the center of the trachea because of the pressure differential. Eventually the two vocal folds will meet at the midline and the airflow will cease. The vocal folds are adducted to the midline and are firmly held there. Air from lungs cause subglottic pressure which overcomes resistance of the adducted folds, release a puff of air. The air stream flows through an hourglass-shaped area.
Wider portions are the trachea and pharynx.
The middle is the channel bounded by the true and false cords. This completes a vocal fold cycle. In this model respiration is the driving force that sets the vocal folds into motion and the interchange between pressure and flow at three critical sites keeps the vocal folds vibrating. The leading edge is set into motion by the air from the lungs. Then negative as the folds recoil to midline.