Final answer:
The Myoelastic-Aerodynamic Theory describes how vocal folds open and close and produce sound due to a combination of muscular forces (myoelastic) and airflow (aerodynamic) resulting in their vibration.
Step-by-step explanation:
The Myoelastic-Aerodynamic Theory explains the process by which the vocal folds (VF) open and close as a result of myoelastic and aerodynamic forces. During phonation, the VF adduct and airflow from the lungs creates a pressure buildup beneath them. This pressure, in conjunction with the elasticity of the VF and their muscle tension, leads to a rhythmic opening and closing. As air rushes past the VF, it causes them to vibrate, and these vibrations are then modified by the vocal tract to produce sound. Changes in pitch occur through adjustments in muscle tension, altering VF tension, while loudness increases with stronger airflow, which increases the amplitude of the sound pressure waves.