What stimulates hearing and balance in the inner ear?

The correct answer centers on the essential role of fluid movement in the inner ear, specifically within the cochlea and the vestibular system. The inner ear contains structures such as the cochlea, which is responsible for hearing, and the semicircular canals, which are vital for balance.

When sound waves enter the ear, they create vibrations that travel through the middle ear and into the inner ear. In the cochlea, these vibrations cause the fluid within to move. This movement of fluid stimulates hair cells, which are sensory receptors that convert mechanical energy into electrical signals. These electrical signals are then transmitted to the brain, allowing us to perceive sound.

Similarly, the vestibular system, which is crucial for balance, also relies on the movement of fluid within the semicircular canals. As the head moves, the fluid shifts, stimulating the hair cells and sending information about the body's position and motion to the brain.

Thus, fluid movement across nerve sensors in the inner ear is fundamental for both hearing and balance, making it the correct response. This differentiates it from other options that do not accurately capture the physiological process involved in auditory and vestibular stimulation.