How the ear works
Why do we hear?
Different levels of hearing were first noticed at the close of World War II by Dr Ramsdell while he was working in Deshon Army Hospital in Butler, Pennsylvania, which was a veteran’s Administration Hospital.
He had the opportunity to observe young adults who had lost some or all of their hearing whilst on active service, and recognised the four stages of how we use our hearing, particularly the importance of the ‘feeling of oneness with an active environment’. These young adults constantly complained that the world seemed dead.
Ramsdell became aware that we rely on our hearing for:
- understanding speech – the symbolic level. Informs, educates and entertains.
- appreciating sounds that please us – the aesthetic level. Gives pleasure.
- recognising sounds that alert us – the warning level. Alerts and prepares.
- recognising the changing background sounds of the world around us – the primitive level. Auditory background for daily living.
How does this work in practice?
You are sitting in a room near an open window which looks out onto a busy road. The sound of traffic is comforting or irritating depending your your reaction to the noise. All the same you know you can hear it. Primitive level.
You remember that you have forgotten something for a meal you are making and you decide to drive to a local shop. You listen to the car radio which tells you that the traffic is heavy on the main road. Sure enough, the noise of the traffic is louder as you approach. The spoken word and the background sound mean the same thing – heavy traffic. Symbolic level.
You hear a siren and know that you will need to pull over and wait for the emergency vehicle to pass. This is because the sound of the siren has alerted you and given you an instruction. Warning level.
How does normal hearing work?
The three parts of the ear anatomy are the outer ear, the middle ear and the inner ear. The inner ear is also called the cochlea. (‘Cochlea’ means ‘snail’ in Latin; the cochlea gets its name from its distinctive coiled up shape.)
- The outer ear consists of the pinna, ear canal and eardrum
- The middle ear consists of the ossicles (malleus, incus, stapes) and ear drum
- The inner ear consists of the cochlea, the auditory (hearing) nerve and the brain
Sound waves enter the ear canal and make the ear drum vibrate. This action moves the tiny chain of bones (ossicles - malleus, incus, stapes) in the middle ear. The last bone in this chain ‘knocks’ on the membrane window of the cochlea and makes the fluid in the cochlea move. The fluid movement then triggers a response in the hearing nerve.
Diagram of the human ear
What happens when you have problems with hearing?
When your hearing is working normally, information is being passed through the different parts of the ear to the brain. The type of hearing problem you may have depends on which part of the ear is not responding well.
Outer ear or middle ear problems lead to inefficient transfer of sound. The cochlea is still working but may not receive enough information. This type of hearing loss is called conductive hearing loss. The problem is that the sound is not being conducted (transferred) well enough. Conductive deafness can be caused by things such as an ear infection, a hole in the eardrum or otosclerosis.
An inner ear (cochlear) problem means that sound arrives at the cochlea, but is then not fully passed on to the hearing nerve. Also it is possible that the hearing nerve itself is not passing on information well, or fails to pass on the sound at all. A cochlear or neural hearing loss is called a sensorineural hearing loss. Sensorineural hearing loss can be caused by things such as old age, Ménière’s Disease or loud noise.
It is possible to have a mixed hearing loss with both a conductive and sensorineural element.
Video of how the ear works: thanks to MED-EL