Audiometric screening services

Ears are our organs of hearing. They are also part of the mechanism that controls our balance. If you look at the diagram later on, you will see that an ear can be divided into three sections:

The outer ear

The outer ear consists of the pinna, which is the part you can see, and the external auditory canal, which is the passage that sounds travel along. This canal is about 2.5 cm long and lined with skin. If you look at someone's ear from the side, you can see the entrance to it. The part of the canal near the outside has hairs, and glands which produce wax. Together these keep it clean. The other end of the canal is covered by the eardrum - the tympanic membrane. When sound reaches the eardrum from the outside, it vibrates. Beyond the eardrum is the middle ear.

The middle ear

The middle ear is a space or cavity about 1.3 cm across, filled with air. The air travels to it along the eustachian tube, which connects the cavity with your nose and throat. Most of the time the tube is closed, but if you yawn, swallow or blow your nose it opens. You may notice a clicking sound in your ear when this happens; this is normal.

Between the middle ear and the inner ear is a wall of bone which has two small openings in it, the oval window and the round window, each sealed by a membrane. A chain of three tiny bones stretches right across the middle ear cavity to conduct sound from the eardrum to the oval window, and from there into the inner ear. These three bones, the ossicles, are called the malleus, the incus and the stapes. You may also have heard them called the hammer, anvil and stirrup.

The malleus is attached to the inner side of the eardrum, the incus stretches between the malleus and the stapes, and the base of the stapes fits into the oval window. When sound enters your ear and makes the eardrum vibrate, the vibrations pass from the eardrum along the ossicles. The stapes pushes like a little piston against the membrane in the oval window. Behind the oval window is the inner ear.

The inner ear

The inner ear has two parts: the cochlea and the semicircular canals. Both are embedded in bone. The cochlea - the hearing part - is a spiral tube about 3.5 cm long which coils 2.75 times.

The spiral is divided lengthwise into two fluid-filled chambers, the outer one of which starts at the oval window, continues to the tip of the cochlea and then doubles back, ending at the round window. The vibrations caused by sound pass from the stapes, through the oval window and into the fluid in the outer chamber.

The central chamber of the cochlea contains the Organ of Corti. This has about 17,000 small hair cells covered with tiny hairs. Hair cells are connected to the auditory nerve, also called the nerve of hearing, which goes from the cochlea to your brain. When sound waves enter the fluid of the cochlea, they move the hair cells and these send electrical messages to the auditory nerve. Different

frequencies of sound are picked up by different hair cells, depending where in the spiral tube they are located. The nerve passes impulses up to your brain which recognizes them as different sounds - for example people talking, or footsteps.

The semicircular canals are not used for hearing - they are part of your balance system. They are filled with fluid and have hair cells rather like those in the cochlea. When you turn your head, the fluid in the canals moves and the tiny hairs on the nerve endings bend. Nerve impulses travel to your brain, giving information about the direction in which your head is moving.

Sound goes into the outer ear, passes through the middle ear and is processed by the inner ear before being sent to your brain. If you are deaf or hard of hearing, it is because part of this system does not work.

If you suffer from dizziness, this may sometimes be caused by problems in the inner ear.

Ears are delicate and complex structures that are easy to damage and we develop a hearing loss if any part of the mechanism of the ear does not work. Hearing losses are classed as 'conductive' or 'sensorineural' depending on which part of the ear is not working properly.

A conductive hearing loss is caused by a mechanical obstruction to the transmission of sound in the outer or middle ear. A sensorineural loss is caused by a problem in the inner ear, usually in the hair cells of the cochlea but sometimes in the nerve pathways to the brain. Some people have a 'mixed' hearing loss - conductive and sensorineural.

Hearing loss ranges from mild to profound or total deafness. Its level can be determined by hearing tests. Various terms, such as high frequency, low frequency or flat - meaning a similar hearing loss across all normally heard frequencies - may be used to describe it, depending on the pattern of hearing loss. It may have various causes, many of which produce a characteristic type and degree of loss.

Sensorineural deafness

Most types of sensorineural deafness are caused by damage to the hair cells in the cochlea. These cells cannot be repaired or replaced. Damage of this kind may happen if you have an infection, or if you need to take particular drugs such as streptomycin or gentamicin. It is also an effect of growing old. In addition, the cochlea can be permanently damaged by exposure to loud noises. It is important to be aware of the dangers and know how to minimize risk to your hearing.

Hearing loss caused by noise

Exposure to excessive noise can cause two main types of hearing loss, temporary threshold shift and permanent threshold shift.

Temporary threshold shift

This is most commonly noticed as a temporary dullness in hearing after you have been exposed to loud noise. Your hearing will subsequently recover but how long this takes will depend on factors such as the loudness and how long you were exposed to the noise.

Permanent threshold shift

If your hearing does not recover completely after about 48 hours, the remaining loss is considered to be permanent. There are two categories of permanent threshold shift:

Noise-induced or occupational hearing loss happens when you have been regularly exposed to hazardous levels of noise over a long period of time. You gradually acquire a sensorineural hearing loss which is usually most severe in the high frequencies at around 3-4 kHz. The hearing loss will be similar in each ear and will initially get worse if you continue to be exposed to the noise.

Practical effects of noise-induced hearing loss

If you suffer from hearing loss caused by noise exposure, tests will normally show your hearing loss to have a characteristic pattern. The typical pattern usually consists of a dip in your hearing in the high frequencies - at around 3-4 kHz. If the noise exposure continues, this notch in your audiogram - the chart that shows your hearing levels when you have a hearing test - will broaden and spread to affect lower and higher frequencies too. The hearing loss will continue to increase for up to about five years, after which it gradually stops getting worse unless you are exposed to increased noise levels. People are often unaware of a hearing loss, particularly to begin with. As it gets worse and spreads to affect a wider frequency range, you may then be aware of difficulty in following conversations if there is background noise.

Lets take a closer look at the ear....................

TINNITUS

Introduction
Exposure to loud noise is one of the most common causes of tinnitus, the buzzing, whistling or other noises that some people hear in their ears or head. Excessive noise at work, at home, or during leisure activities can mean not only that you develop a hearing loss, but also that the permanent damage caused to your hearing system may result in the onset of tinnitus, sometimes years after the period of noise exposure. Sometimes persistent tinnitus is the first sign that the ear has been damaged by noise. Tinnitus can occur before there is any noticeable effect on hearing.

Loud continuous noise damages the sensitive hair cells in our inner ears. The damage affects the sensitivity of our hearing and is irreversible; cells killed by loud noise cannot be replaced. We may also develop tinnitus as a result, and the tinnitus may be more disturbing than the hearing loss itself.

The louder the noise is and the longer you are exposed to it, the greater the risk. If you have to be in a very noisy situation, always protect your ears with plugs or muffs and get away from the noise as quickly or as often as you can.

At home
Most domestic noise is at acceptable levels, but you should be aware of the potential harm in:

· loud music - turn it down or move yourself or the speakers.

· personal stereos - turn the volume down, use them less, or use them against fewer and quieter background noises. Use the volume-limiting facility there is one.

· DIY equipment such as electric drills, saws, grinders, sanders - use ear protectors - muffs, not just ear plugs.

· loud noise from televisions, radios and computer games.

· noisy toys - at arm's length, model aeroplanes have been known to emit high pitched sounds of 112 dBA; toy mobile telephones have been recorded at 122 dBA at the ear and toy weapons can be even louder. Children's hearing is particularly vulnerable to noise.

Leisure time
Many people pursue noisy sporting or social activities. You should wear specially designed ear protectors if you are firing guns or standing near to people who are.

We have legal protection from noise at work, but this does not cover noisy situations we may find ourselves in outside work. For example, if you work in a noisy bar or club, the Noise at Work Regulations protect you, but if you go to the same bar or club after work as a customer, they do not. Regular exposure to such noise may mean you suffer damage to your ears which you are not aware of until you are older.

LOOK AFTER YOUR HEARING