Final answer:
During the pharyngeal phase of swallowing, the tongue is pressed against the roof of the mouth, which prevents food from going back into the mouth, while the soft palate elevates to block off the nasopharynx.
Step-by-step explanation:
During the pharyngeal phase of swallowing, the tongue is pressed against the roof of the mouth to prevent food from re-entering the mouth, and the soft palate (velum) elevates to occlude the nasopharynx.
The pharyngeal phase is a critical part of the swallowing process. Once the voluntary phase, where you control swallowing, ends, the pharyngeal phase begins involuntarily. Triggered by receptors in the oropharynx, neural impulses are sent to the deglutition center in the medulla oblongata, which coordinates the necessary actions. During this phase, the soft palate and uvula rise reflexively, closing off the nasopharynx to prevent food from entering the nasal cavity. Concurrently, the epiglottis folds over the trachea to prevent food from entering the airway, and the pharyngeal constrictor muscles propel the food bolus into the esophagus.