Final answer:
In the pharyngeal phase of swallowing, impulses sent from receptors in the oropharynx to the medulla oblongata initiate the pharyngeal swallow response. This phase involves the movement of the soft palate and uvula to close off the nasopharynx and the constriction of laryngeal muscles to prevent food from entering the trachea.
Step-by-step explanation:
In the pharyngeal phase of swallowing, the stimulation of receptors in the oropharynx sends impulses to the deglutition center in the medulla oblongata. These impulses then cause the soft palate and uvula to move upward and close off the nasopharynx, preventing food from entering the respiratory pathways. Additionally, the laryngeal muscles constrict to further block food from entering the trachea.