Final answer:
The tensor veli palatini muscle elevates the soft palate during the voluntary phase of deglutition to prevent food from entering the nasal cavity and helps in equalizing middle ear pressure by opening the Eustachian tubes.
Step-by-step explanation:
The action of the tensor veli palatini muscle is crucial in swallowing and middle ear function. This muscle originates from the sphenoid bone and the cartilaginous portion of the auditory tube. Its action involves the voluntary phase of deglutition, where it contracts to elevate the soft palate, which in turn helps prevent the movement of food into the nasal cavity during swallowing. Additionally, during the voluntary contraction related to Valsalva's maneuver, the tensor veli palatini plays a role. As a synergist muscle, it also assists by opening the Eustachian tubes, allowing for equalization of pressure in the middle ear.