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Humans create most speech by exploiting the outgoing airstream during pulmonary ventilation. The structures used for this purpose are shown in Figure 2.2. During the process, carbon dioxide and oxygen are exchanged in the lungs through a two‐phase cycle of inspiration and expiration. To initiate typical inspiration, the diaphragm is lowered, causing the thoracic cavity—the chest—to expand. As a result of the increase in available volume, air pressure in the chest drops, and air rushes in through the nasal cavity to fill the lungs. The reverse phase, expiration, is partly caused by relaxation of the diaphragm, which decreases the size of the chest cavity. This increases the thoracic air pressure so that air moves outward. Most speech is produced using this outward airflow and is therefore said to entail a PULMONIC EGRESSIVE airstream. By this, we simply mean that the source of airflow for the speech is the lungs (pulmonic), and the direction of the flow is outward (egressive).

Figure 2.1 The “chain” connecting speaker and listener during speech

Figure 2.2 Structures used during pulmonary ventilation

(Source: Adapted from https://commons.wikimedia.org/wiki/File:Blausen_0770_RespiratorySystem_02.png)

During expiration, air moves from the lungs upward through the bronchi and TRACHEA. It then passes through the larynx and the PHARYNX, and finally exits through the ORAL CAVITY, the nasal cavity, or both. Speech production requires some careful but unconscious management of the breathing mechanism. In fact, we breathe much differently when we speak than when we are quiet. For one thing, the inspiratory phase is faster during speech, and expiration is much more prolonged. We are normally unaware of the difference, however, and we usually manage to utter all the words we have planned without needing an awkward break to inhale partway through.