Valve hypothesis

Valve 1: glottal fold adduction and abduction (dd = together; bd  = apart)
Valve 2: partial covering and damping of the adducted glottal vocal fold vibration by the ventricular (false) folds; ventricular incursion
Valve 3: sphinctric compression of the arytenoids and aryepiglottic folds forwards and upwards by means of the thyroarytenoid muscle complex. (narrow, wide AES)
Valve 4: retraction of the tongue and epiglottis moving backwards and downwards, culminating in extreme cases  in full closure onto the pharyngeal wall, by means of the hyoglossus muscles (epiglotto-pharyngeal constriction)
Valve 5: laryngeal raising and lowering (larynx height: low, mid and high)
Valve 6: inward constriction of the pharynx walls due to the sphincteric action of the superior, middle, inferior pharyngeal constrictors (pharyngeal narrowing)

Source: John Esling's paper