What are two primary theories explaining the production of vocal fold vibration?

The two primary theories that explain the production of vocal fold vibration are the Myoelastic-Aerodynamic theory and the Neurochronaxic theory.

The Myoelastic-Aerodynamic theory is fundamental in understanding how vocal folds vibrate during phonation. This theory combines the concepts of muscle elasticity (myoelastic) and the aerodynamics of airflow. When air is expelled from the lungs and passes through the closed vocal folds, it creates a drop in pressure (according to Bernoulli's principle). This drop in pressure, combined with the elasticity of the vocal folds, causes them to open and close rapidly, resulting in vibration. This cycle of opening and closing produces sound waves, which articulate speech sounds.

The Neurochronaxic theory, proposed by some researchers, suggests that each cycle of vocal fold vibration is controlled by neural signals that stimulate the muscles involved in phonation. However, this theory is more controversial and less widely accepted than the Myoelastic-Aerodynamic theory. It emphasizes the timing of neural impulses in relation to vocal fold movement rather than physical properties alone.

Together, these two theories provide a comprehensive understanding of how vocal fold vibration occurs, explaining both the mechanics of sound production and the neural control of voice.