Final answer:
The Eustachian tube is responsible for ventilating the middle ear to maintain equal air pressure on both sides of the tympanic membrane.
Step-by-step explanation:
The part of the ear that ventilates the middle ear to keep pressure normal is the Eustachian tube. This small passage connects the middle ear to the nasopharynx and allows for the equalization of air pressure on both sides of the tympanic membrane, also known as the eardrum. Without the proper function of the Eustachian tube, individuals might experience discomfort or problems with hearing, as the pressure difference can hinder the eardrum's ability to vibrate normally.