To understand velopharyngeal function, it is important to know about the structures in the mouth. Figure 1 shows the structures of the roof of the mouth: the hard palate and the soft palate. The soft palate is also called the velum. This figure also shows the tonsils, which are toward the back of mouth on each side.
During normal speech, air from the lungs and sound from the vocal cords (in the larynx or “voice box”) travel upward in the throat (pharynx). To produce most speech sounds, the air and sound need to be directed into the mouth and blocked from entering the nasal cavity. This is done through closure of the velopharyngeal valve.
The velopharyngeal valve consists of the following structures:
- Velum (soft palate)
- Lateral pharyngeal walls − side walls of the throat
- Posterior pharyngeal wall − the back wall of the throat
Figure 2 shows the velum resting against the back of the tongue during normal nasal breathing. During inhalation, air can flow through the nose and pharynx down to the lungs without obstruction. Exhalation of carbon dioxide follows the same path in reverse.
Figure 3 shows how the velum rises to close against the posterior pharyngeal wall during speech. At the same time, the lateral pharyngeal walls (not shown in the diagram) move to close against the soft palate. This results in a sphincter-type closure. Velopharyngeal closure also occurs during swallowing, gagging, vomiting, sucking, blowing and whistling.