The cochlea is a small, spiral part deep in the inner ear — not the flap on the side of your head, and not the tube just inside it, but the hidden part that does the real work of hearing. It is shaped like a snail shell, and that shape is the whole point of the name. Sound from outside makes liquid inside the cochlea move; tiny hair cells there turn that movement into signals, and the signals go to the brain, which is how you hear pitch and detail. If this part is damaged, a person may not hear well even if the outer ear looks fine. Doctors talk about a cochlear implant when they mean a device that tries to help if the cochlea itself cannot do the job.

耳蝸