Which structure acts to equalize pressure between the middle ear and the throat?

• A. Ear canal
• B. Eustachian tube
• C. Cochlea
• D. Semicircular canals

Answer: (B)

The key idea is how the ear equalizes pressure as conditions change. The Eustachian tube connects the middle ear to the throat and acts as a pressure equalizer. It stays mostly closed, but when you swallow, yawn, or chew, the muscles open it briefly, allowing air to flow between the middle ear and the throat. This balances the air pressure on both sides of the eardrum, so it can vibrate properly and you don’t feel painful pressure—something that’s especially noticeable during airplane takeoff/landing or scuba diving. The ear canal just carries sound to the eardrum; the cochlea is the hearing part of the inner ear; the semicircular canals are involved in balance. So the Eustachian tube is the structure that equalizes pressure between the middle ear and the throat.