Final answer:
During the pharyngeal stage of swallowing, the soft palate and levator muscles contract to close off the nasopharynx and lift the larynx, preventing food aspiration and temporarily halting respiration. This helps food pass safely from the mouth to the esophagus.
Step-by-step explanation:
In the pharyngeal stage of swallowing, the soft palate and levator muscles contract to raise the soft palate and block the nasal cavity, ensuring that a bolus of food can pass safely into the esophagus without entering the nasopharynx or the respiratory tract. This movement, along with the rising of the uvula, closes off the entrance to the nasopharynx, and the larynx is simultaneously lifted to prevent aspiration. The laryngeal muscles tighten, and deglutition apnea occurs, temporarily halting respiration. The pharyngeal constrictor muscles then contract, helping the bolus move through the oropharynx and into the laryngopharynx, until the relaxed upper esophageal sphincter permits the bolus to enter the esophagus.
This series of complex neuromuscular actions during the pharyngeal stage is critical for the safe passage of food from the mouth to the stomach, effectively separating the digestive and respiratory pathways when food is being swallowed.