The three fluid-filled tubes in the inner ear that send information to the brain in order to maintain balance are the?

• A. Eustachian Tube
• B. Pinna
• C. Oval Window
• D. Semicircular Canal

Answer: (D)

Balance relies on the vestibular system, and the three fluid-filled tubes in the inner ear that detect head rotation are the semicircular canals. Each canal is filled with endolymph, and when you move, the fluid lags behind the motion. This causes movement of hair cells in the sensory region called the crista ampullaris inside the ampulla, which generates nerve signals sent to the brain about angular velocity. Because there are three canals oriented in different directions, they sense rotation around three spatial axes, helping you maintain balance and stable gaze.

The other structures listed don’t provide rotational balance information: the Eustachian tube mainly equalizes middle-ear pressure; the Pinna is part of the outer ear that collects sound; and the Oval Window is the membrane that transmits middle-ear vibrations into the inner ear.