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Outer ear Hearing begins with the outer ear (most commonly referred to as the pinna) which, due to its unique shape, collects and focuses the incoming sound waves into the external auditory canal where they travel along until reaching the eardrum. Middle ear When the sound waves hit the eardrum it causes it to vibrate. These vibrations are passed onto the inner ear by way of the auditory ossicles which is made up of the three smallest bones in the body, the malleus, incus and stapes (commonly referred to as the hammer, anvil and stirrup). The malleus is attached to both the eardrum and incus which is then connected to the stapes. The footplate of the stapes then fits into the oval window which forms the boundary between the middle and inner ear. Also situated in the middle ear is the eustachian tube which is connected to the throat and keeps the air pressure in the middle ear the same as that outside. Inner ear When the footplate of the stapes moves back and forth it creates motion in the fluid which fills the cochlea. This stimulates the tiny hair cells situated along the length of the cochlea which send nerve impulses to the brain via the auditory nerve where they are finally interpreted as sound. Another important part of the inner ear is the semicircular canals. Whilst they do not have anything to do with how we hear, they are responsible for our sense of balance. |
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