Which trio of bones in the middle ear amplifies sound?

• A. Hammer, Anvil, and Stirrup
• B. Hammer, Anvil, and Cochlea
• C. Hammer, Incus, and Stapes
• D. Hammer, Cochlea, and Vestibule

Answer: (C)

The middle ear uses a tiny lever system to boost the force of vibrations before they enter the fluid-filled inner ear. The three bones that do this are the hammer (malleus), the anvil (incus), and the stirrup (stapes). The eardrum’s vibrations move the hammer, which passes the motion to the anvil, and then to the stirrup, which presses on the oval window of the cochlea. Because the eardrum covers a relatively large area while the oval window is much smaller, this arrangement concentrates the energy into a higher pressure at the inner-ear input. The lever action of the bones also contributes to this pressure boost, helping overcome the impedance difference between air and the cochlear fluids. All of this is why the trio of hammer, anvil, and stirrup is described as amplifying sound. The other options mix in inner-ear structures like the cochlea or vestibule, which aren’t the middle-ear bones responsible for this amplification.