Normal hearing occurs when sound travels to the outer ear, goes through the ear canal and reaches the tympanic membrane. The tympanic membrane is the start of the middle ear. The tympanic membrane vibrates in response to the sound and this causes vibration in the chain of the three bones in the middle ear.( malleus , incus and stapes = ossicular chain) The vibration is transferred to the inner ear or cochlea. The cochlear consists of nerve fibres (hair cells) that receive sound. Different hair cells are responsible for receiving different pitches of sound.The signal is transferred via the auditory nerve to a nucleus in the brainstem, which, if it receives a signal from both ears, can:
> Know the direction of sound.
> Boost speech above background noise
>Help with perceptions of balance
Then, it is transferred to the auditory cortex in the thinking brain, where the signal’s message is understood.