Cochlea to structures in the brainstem for further processing. The "stapes" (stirrup) ossicle bone of the middle ear transmits vibrations to the "fenestra ovalis" (oval window) on the outside of the cochlea, which vibrates the perilymph in the "vestibular duct" (upper chamber of the cochlea). The ossicles are essential for efficient coupling of sound waves into the cochlea, since the cochlea environment is a fluid–membrane system, and it takes more pressure to move sound through fluid–membrane waves than it does through air; a pressure increase is achieved by the area ratio of the tympanic membrane to the oval window, resulting in
Evolution of the cochlea mammals. Prestins are located in the outer hair cells of mammalian cochlea and are considered motor proteins. They are found in the hair cells of all vertebrates, including fish, but are thought to have initially been membrane transporter molecules. A high concentration of prestins are found only in the lateral membranes of therian outer hair cells (there is uncertainty with regard to concentrations in monotremes). This high concentration is not found in inner hair cells, and is also lacking in all hair cell types of non-mammals. Prestin also has a role in motility, which evolved a greater importance in the