Airflow occurs when an air valve is open and there is a pressure difference between the connecting cavities. When an air valve is closed, there is no airflow. The air valves are the vocal folds (the glottis), which regulate between the supraglottal and subglottal cavities, the velopharyngeal port, which regulates between the oral and nasal cavities, the tongue, which regulates between the oral cavity and the atmosphere, and the lips, which also regulate between the oral cavity and the atmosphere.