Thursday 27 February 2014
Hearing damage
Damage to the structures or nerve fibres of the ears and/or
the brain caused, for example, by illness, physical trauma or natural aging,
may result in hearing loss. It is,
therefore, important to be aware of the many different factors that can cause
such damage.
Here I have listed a few:
- Illness such as
measles and meningitis may cause damage to the auditory nerve or cochlea.
- Chemicals such as lead, some solvents and some
asphyxiants, may damage the cochlea with
lesions.
- Some medications,
for example Aminoglycoside antibiotics and salicylates (aspirin), can
cause damage with prolonged use.
- Trauma, including
punctured ear drum from foreign objects, fractures of the temporal bone and
knocks to the head, can cause temporary or permanent damage depending upon the
severity.
- A blockage or
deformity in the middle ear can prevent the bones from vibrating properly.
However, noise is the cause of about half of all cases of
hearing loss and noise damage in young people today is of particular concern.
How noise-induced hearing loss occurs:
Permanent damage to your hearing can happen very quickly with
exposure to loud noises such as fire arms.
Any sounds above 90 decibels
are extremely dangerous. So, sustained exposure to anything as loud as even a lawnmower could
cause serious damage.
Listening to
music on headphones can be very bad for your hearing. In fact,
listening to loud music on headphone can be one of the quickest ways to cause
serious, permanent damage.
How to avoid noise damage:
If the noise is above 85db make sure you
turn it down or wear ear protectors.
If you go to concerts or nightclubs wear earplugs and don’t stand
near to the speakers.
Lower the volume of your stereo/TV etc.
The three main sections of the ear
The ear is made up of three different
parts - the outer ear, the middle ear and the inner ear.
The outer ear is made up of the pinna,
a flesh covered cartilage appendage that can be seen on either side of the
head, and the ear canal, which is about 2cm long. These structures receive and
direct sound waves to the eardrum. When sound goes through the outer ear it is
still a mechanical wave,
an oscillating pattern of high and low pressure states.
The middle ear is a cavity filled with
air that contains the eardrum, a tightly stretched membrane at the edge of the
outer and middle ear, and three very small bones - the hammer, anvil and
stirrup. When sound waves reach the ear drum, compression pushes it inward and
rarefaction pushes it outward, causing it to vibrate at the same frequency as
the sound waves. This mechanical vibration then causes the hammer, the anvil
and the stirrup to vibrate at the same frequency. Because of the way these
bones are organised, the vibration in the stirrup is greater than that of the
hammer. Also, pressure waves coming into contact with the relatively large
eardrum is concentrated as it is transformed into internal vibrations of the
bones so that the force vibrating the stirrup is around fifteen times stronger.
In these ways, the three small bones in the middle ear are able to amplify the
vibrations of the sound waves.
The inner ear is made up of a cochlea,
a small organ shaped a bit like a snail, the semi-circular canals, and the
auditory nerve. The cochlea is filled with fluid and its inner surface is lined
with over 20 000 hair-like nerve cells which play one of the most important
parts in our ability to hear. As the
stirrup is connected to the inner ear, vibrations travel from it to the fluid
of the inner ear and transform into compression waves which then bend the
hair-like nerve cells, causing most of them (the outer ones) to tremble and
shake. This makes the vibrations stronger and stronger. This increased
vibration causes the remaining (inner) hair cells to release an electrical
impulse that is sent via the auditory nerve to the brain. The brain is then
capable of making sense of these nerve impulses and of interpreting what has
been heard.
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