Final answer:
The 4 key structures that keep the airway closed during swallowing or open during breathing are the soft palate, uvula, larynx, and the epiglottis.
Step-by-step explanation:
The 4 key structures that keep the airway closed during swallowing or open during breathing are the soft palate, uvula, larynx, and the epiglottis. During swallowing, the soft palate and uvula rise reflexively to close off the entrance to the nasopharynx, while the larynx is pulled superiorly and the epiglottis folds inferiorly, effectively closing off the glottis and preventing food from entering the trachea. During breathing, these structures remain open to allow air to pass freely through the airway.