How do the three tiny middle-ear bones help mammals hear?

The three tiny middle-ear bones—the malleus (hammer), incus (anvil), and stapes (stirrup)—are essential for mammalian hearing because they function as a mechanical lever system.123

These ossicles form a chain that bridges the middle ear, connecting the tympanic membrane (eardrum) to the inner ear. When sound waves strike the eardrum, they cause it to vibrate; the ossicular chain then transmits and amplifies these vibrations to the fluid-filled cochlea. The efficiency of this sound transmission is determined by the lever ratio of the bones and the difference in surface area between the eardrum and the stapes footplate, which rests in the oval window of the cochlea.123

Additionally, two small muscles—the tensor tympani and stapedius—can contract to adjust the tension and stiffness of this chain, protecting the inner ear from damage caused by excessively loud sounds.12