Illustration of the normal ear canal. The inner ear contains a maze of fluid-filled passages called the labyrinth. The cochlea is a hollow spiral containing microscopic hairs that respond to sound vibrations conveyed from the middle ear. The near end of the spiral picks up high-frequency sound; the central (far) end detects low frequency sound. Nerves connected to the cochlea carry sound impulses to the brain. The semi-circular canals provide the sense of balance by detecting movement of fluid through the three planes.