The inner ear includes a tiny coiled tube, called the cochlea, which is the organ of hearing. It also has some other structures that help us maintain our balance.
The cochlea is filled with fluid and thousands of tiny hair cells (sensory cells).
Movement of the middle ear bones pushes on a little membrane at the entrance of the cochlea called the oval window. This causes the fluid inside the cochlea to move. When this fluid moves, the hairs bend, converting the movement into electrical signals. These electrical signals are passed along the auditory nerve to the brain. The brain interprets this as sound.