Cochlea a protein motor called prestin on their outer membranes; it generates additional movement that couples back to the fluid–membrane wave. This "active amplifier" is essential in the ear's ability to amplify weak sounds. The active amplifier also leads to the phenomenon of soundwave vibrations being emitted from the cochlea back into the ear canal through the middle ear (otoacoustic emissions). Otoacoustic emissions are due to a wave exiting the cochlea via the oval window, and propagating back through the middle ear to the eardrum, and out the ear canal, where it can be picked up by a microphone. Otoacoustic emissions
Evolution of the cochlea (lower frequency) papillae, but it is uncertain whether either is homologous to the hearing organs of lepidosaurs, archosaurs and mammals and we have no idea when they arose. Fish have no dedicated auditory epithelium, but use various vestibular sensory organs that respond to sound. In most teleost fishes it is the saccular macula that responds to sound. In some, such as goldfishes, there is also a special bony connection to the gas bladder that increases sensitivity allowing hearing up to about 4 kHz. The size of cochlea has been measured throughout its evolution based on the fossil record. In one