Air-filled tube of the middle ear that equalises pressure between the external and internal ear.

• A. Tympanic membrane
• B. Auditory canal
• C. Eustachian tube
• D. Oval window

Answer: (C)

Pressure regulation between the outside environment and the middle ear is achieved by an air-filled passage that connects the middle ear to the back of the throat. This passage, the Eustachian tube, opens briefly during swallowing or yawning, allowing air to flow and equalize the pressure on both sides of the eardrum. Keeping the middle ear pressure similar to ambient pressure prevents the tympanic membrane from bulging or bursting as you experience changes in altitude or underwater depth. It’s normally closed and lined with mucous membrane, opening when needed to balance pressure.

The tympanic membrane, or eardrum, is the vibrating surface of the middle ear. The auditory canal is the external ear passage that channels sound to the eardrum. The oval window is a membrane that transmits vibrations from the middle ear to the inner ear.