Pathology of the Ear - Index
The ear is a wonderful human instrument of
hearing and is made up of three main parts - an outer, a middle and an inner
When all these parts are working properly we can hear sounds ranging from the roar of a lion to the ticking of the tiniest watch.
The outer ear consists of the auricle, or structure of skin and gristle that projects from the side of the head, and a short canal leading to the middle ear.
The lining of this canal has small glands which produce wax that protects the ear by keeping outer dust and other harmful things.
The inner end of the canal is closed by a membrane called the ear-drum.
It is sensitive to sound waves, vibrating when they hit it.
The middle ear lies on the other side of this membrane and is a small cavity, or space, in the bone of the skull.
Directly behind the drum are three curious little bones called the hammer, the anvil and the stirrup, because they look like these things.
They magnify the vibrations of the drum and pass them on to the inner ear.
A tube known as the Eustachian tube, runs from the middle ear to the back of the nose and allows air to reach the middle ear inside the ear-drum.
As air is always pressing on the drum from outside it is most important to have air inside it as well, otherwise it would be pushed inwards all the time and be unable to vibrate.
It is also important that the pressure of the air inside the drum should be the same as that outside.
If the pressure outside changes suddenly, as when people are taking off or landing in an aircraft, they become temporarily deaf.
(Air pressure decreases the higher one goes and increases again as one returns to the sea level).
They are therefore told to swallow, as this opens the Eustachian tube and lets air from outside into the middle ear.
When the pressure on both sides of the drum becomes equal again they can hear normally.
The inner ear consists of two separate parts.
The cochlea, which looks like a snailís shell (and takes its name from the Latin word for snail), is filled with fluid and also contains very fine nerves which communicate with the brain.
The fluid catches the vibrations of the three little bones of the middle ear and passes them on to the nerves which send them to the brain.
The other part of the inner ear is concerned with balance and not with hearing.
It contains three semicircular canals filled with fluid; together with sight they give the feeling of balance.
If they are out of order people become dizzy and unable to work properly.
The canals are easily upset by the movement of the boat and when that happens seasickness follows.
Sound is the impression made on us when waves of air strike the ear-drum and end as a message in the brain.
These waves can neither be seen nor felt but the ear is so delicate that it catches all the shades of difference in them.
Only when they reach the brain do we hear anything.
A sound is first caught by that part of the ear which is outside the head and is then sent down the canal to the ear-drum, making it vibrate.
The hammer, anvil and stirrup of the middle ear take up the vibrations, magnify them and pass them on through the fluid of the cochlea to the nerve endings of the inner ear and so to the brain.
When the brain recognizes them we call it hearing.
Deafness may vary from a slight inability to hear small noises to a complete lack of hearing.
It can be caused by a blow on the side of the head, infection inside the ears which may harm either the bones or the soft parts, or by piercing the ear-drum.
Hardened ear wax may also cause deafness but because of the danger of piercing the ear-drum it should be removed only by a doctor.
Exposure to excessive noise levels can also damage a personís hearing.
Much can be done to help deaf people.
They are taught to lip read, or to watch a personís mouth so carefully that they recognize from its shape the words he is using and they often wear hearing aids, which receive and magnify the sounds about them.
Copyright © 2017 histopathology-india.net