The ossicular chain amplifies sound primarily by what mechanism?

• A. Impedance matching between air and inner ear fluids
• B. Creating new neural signals
• C. Filtering out low frequencies
• D. Directly vibrating the tympanic membrane

Answer: (A)

The main idea is that the middle ear boosts sound by impedance matching between air and the cochlear fluids. When a sound wave hits the eardrum, it produces a large displacement over a relatively large area. The ossicular chain then transfers that vibration to the much smaller oval window, which increases the pressure at the fluid boundary. The malleus–incus lever action adds a further boost to force transfer. Together, these mechanisms raise the pressure at the inner-ear fluids by roughly 20–30 dB, helping overcome the big impedance difference between air and the fluid-filled cochlea so more energy enters the inner ear rather than being reflected. The other options don’t capture this primary role: neural signals aren’t generated by amplification at this stage, filtering isn’t the main function of the middle ear, and the tympanic membrane’s vibration alone isn’t what amplifies energy—amplification comes from efficient transfer of energy to the oval window.