SEINDAH KASIHMU

Introduction

Hearing loss is a common problem that often develops with age or is caused by repeated exposure to loud noises.

Hearing loss can occur suddenly, but usually develops gradually. General signs of hearing loss can include:

difficulty hearing other people clearly and misunderstanding what they say
asking people to repeat themselves
listening to music or watching television with the volume turned up higher than other people require

Read more about the symptoms of hearing loss.

When to see your GP

See your GP if you’re having problems with your hearing, or your child is showing signs of hearing difficulty. If you lose your hearing suddenly, in one or both ears, you must see your GP as soon as possible.

Your GP can check for any problems and may refer you to an audiologist (hearing specialist) or an ENT surgeon for further tests.

You can also visit the Action on Hearing Loss website for an online hearing test.

Read more about diagnosing hearing loss.

Parts of the Ear and their Functions

The outer ear

The external part of the ear consists of the pinna and ear lobe.
The pinna or ear shell is the shell-like part of the external ear, and it is made of cartilage and skin. The pinna directs sound waves from the outside into the external auditory canal (ear canal), which in turn channels sound waves to the tympanic membrane (known as the eardrum), causing it to vibrate. The tympanic membrane is a thin, semi-transparent, flexible membrane that separates the outer and middle ear. The outer ear functions to collect sound (acoustic energy), and funnel it to the eardrum (tympanic membrane).

Outer ear

External

Collects sound waves

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Directs sound waves into the ear canal

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Ear canal channels sound waves to the eardrum

The middle ear

The middle ear is an air-filled space that contains three tiny bones known as ossicles which transmit sound. The bones are known individually (according to their shapes) as the:

Malleus (hammer).
Incus (anvil).
Stapes (stirrup).

Sound waves that reach the tympanic membrane cause it to vibrate. In turn, the eardrum sets into motion the first ear bone, which transmits the motion to the second bone (the incus). Finally, the third bone (the stapes) works like a piston to amplify and transform the sound energy into mechanical energy.

This mechanical energy is then transmitted from the stapes to the hearing part (cochlea) of the inner ear via the oval window (a thin membrane between the middle and inner ear).

The middle ear is connected to the back of the nose (nasopharynx) by the Eustachian tube.

The Eustachian tube

The Eustachian tube is a narrow tube that connects the middle ear to the back of the nose and throat. During swallowing, the Eustachian tube opens up to allow air into the middle ear, so that air pressure on either side of the tympanic membrane is the same. In some situations when there is a sudden change in air pressure (for example – during take off and landing in a plane), the pressure in the middle ear is not the same as the outside air pressure. This can make the eardrum bulge or retract and less able to transmit vibrations, causing temporary hearing problems. By swallowing or “popping” the ears, the pressure can again be equalised.

The inner ear

The delicate membranous inner ear (labyrinth) is enclosed and protected by a bony chamber that is referred to as the bony labyrinth. The inner ear contains two main structures:

The cochlea, in the shape of a snail, which is involved in hearing. The round window (fenestra cochlea) is a membrane that connects the cochlea to the middle ear. It helps dampen the vibrations in the cochlea.
The vestibular system (consisting of the semicircular canals, saccule and utricle), which is responsible for maintaining balance and a sense of position.
The cochlea is filled with fluid and contains the organ of Corti – a structure that contains thousands of specialised sensory hair cells with projections called cilia.

The cochlea has approximately 30,000 hearing nerve endings in the hair cells. The hair cells in the large end of the cochlea respond to very high-pitched sounds, and those in the small end (and throughout much of the rest of the cochlea) respond to low-pitched sounds.

These hair cells, and the nerve that connects them to the brain, are susceptible to damage from a variety of causes.

The vibrations transmitted from the middle ear cause tiny waves to form in the inner ear fluid, where they are interpreted as sound. As the stapes pushes back and forth against the cochlea, it compresses the fluid to create waves in the fluid-filled compartments which make the cilia vibrate.

Depending on the characteristics of the waves, specific nerve messages (impulses) are created. The hair cells then convert these vibrations into nerve impulses, or signals, which are sent via the auditory nerve (the hearing branch of the eighth cranial nerve) to the base of the brain (brainstem) and the brain where they are interpreted as sound.

The vestibular system (the semicircular canals, saccule and utricle)

The semicircular canals also contain fluid and hair cells, but these hair cells are responsible for detecting movement rather than sound. As the head moves, fluid within the semicircular canals (which sit at right angles to each other) also moves. This fluid motion is detected by the hair cells, which then send nerve impulses about the position of the head and body to the brain to allow balance to be maintained. The utricle and saccule work in a similar way to the semicircular canals, allowing you to sense your body’s position relative to gravity and make postural adjustments as required.

Why it happens

Hearing loss is the result of sound signals not reaching the brain. There are two main types of hearing loss, depending on where the problem lies:

sensorineural hearing loss – caused by damage to the sensitive hair cells inside the inner ear or damage to the auditory nerve; this occurs naturally with age or as a result of injury
conductive hearing loss – when sounds are unable to pass from your outer ear to your inner ear, often because of a blockage such as earwax, glue ear or a build-up of fluid from an ear infection, or because of a perforated ear drum or disorder of the hearing bones

It’s also possible to have both these types of hearing loss. This is known as mixed hearing loss.

Some people are born with hearing loss, but most cases develop as you get older.

Read more about causes of hearing loss.

Preventing hearing loss

It isn’t always possible to prevent hearing loss if you have an underlying condition that causes you to lose your hearing.

However, there are several things you can do to reduce the risk of hearing loss from long-term exposure to loud noise. This includes not having music or the television on at a loud volume at home and using ear protection at loud music events or in noisy work environments.

You should also see your GP if you have signs of an ear infection, such as flu-like symptoms, severe earache, discharge or hearing loss.

Read more about preventing hearing loss.

Treating hearing loss

The way hearing loss is treated depends on the cause and how severe it is.

In cases of sensorineural hearing loss, there are several options that may help to improve a person’s ability to hear and communicate. These include:

digital hearing aids – which are available through the NHS
bone anchored implants – suitable for people who are unable to use hearing aids and for some levels of sensorineural hearing loss
middle ear implants – suitable for some people who are unable to use hearing aids
cochlear implants – for people who find hearing aids aren’t powerful enough
lip reading and/or sign language – such as British Sign Language (BSL)

Conductive hearing loss is sometimes temporary and can be treated with medication or minor surgery, if necessary. However, more major surgery may be required to fix the ear drum or hearing bones. If conventional hearing aids don’t work, there are also some implantable devices for this type of hearing loss, such as a Bone Anchored Hearing Aids (BAHAs).

Read more about treating hearing loss.

How hearing works

Sound waves enter your ear and cause your eardrum to vibrate. These vibrations are passed to the three small bones (ossicles) inside your middle ear.

The ossicles amplify the vibrations and pass them on to your inner ear where tiny hair cells inside the cochlea (the coiled, spiral tube inside the inner ear) move in response to the vibrations and send a signal through a nerve called the auditory nerve to the brain.

Hearing Disorders