Final answer:
The uvula is part of the soft palate and functions to prevent substances from entering the nasal cavity during swallowing by closing off the nasopharynx.
Step-by-step explanation:
The structure that extends behind the hard palate and snaps over the nasopharynx to prevent substances from moving into the nasal cavity is the uvula, which is part of the soft palate. During swallowing, the soft palate and uvula rise reflexively to close off the nasopharynx, while the larynx is pulled superiorly and the epiglottis folds inferiorly, covering the glottis. This coordinated action prevents food or liquid from entering the nasal or respiratory passages.
The soft palate is a flexible part of the palate that serves as a movable flap that can close the nasopharynx when one swallows. It is mainly composed of skeletal muscle and is located at the posterior end of the mouth. The hard palate, which is anterior to the soft palate, is a bony structure that forms the roof of the mouth and the floor of the nasal cavity. Together, these structures facilitate separating the respiratory and digestive pathways during the process of swallowing, ensuring that ingested materials do not enter the respiratory system.