Sound comes in the form of waves of compressed air, and detecting that sound is wholly dependent on the ear's ability to convert variations in air pressure to chemical signals that can be interpreted by the brain. When sound enters the ear, it deflects the eardrum that lies at the junction of the outer and middle ears. This deflection is then transmitted through the middle ear to a small membrane at the opening of the inner ear, resulting in the formation of waves in the fluid of the inner ear. Those waves flow through the cochlea in a rhythmic fashion and induce parallel deflections in the sensory hair cells that are physically coupled to the cochlea, where the mechanical force translates into a chemical signal.
Stereocilia—bundles of rigid actin filaments—protrude from the ends of the sensory hair cells. They are embedded in a fixed membrane and attached to one another ...
