About Hearing

How the ear hears

In the normally functioning auditory system, the outer and middle ears act as a bridge to transfer acoustic pressure changes (sound waves) to the fluids of the part of the inner ear known as the cochlea. This is accomplished by one of the three small middle-ear bones pushing into and out of the cochlea at a place called the oval window. The cochlea is filled with liquid that carries the vibrations to thousands of tiny hair cells sitting on a membrane that stretches the length of the cochlea. The hair cells on the membrane fire off tiny electrical signals. These electrical signals travel up the cochlea nerves of the auditory pathway to the brain. All this happens in a fraction of a second.

When the hair cells of the cochlea are damaged or missing, the result is sensory hearing loss. However, in most cases, when the sensory cells are damaged there is also some loss of individual nerve fibres. Therefore, this type of hearing impairment is typically called sensorineural, referring to damage to both the sensory end organ and the nerve itself.