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What are the main parts of the ear and their function?

The ear is an organ for hearing and aiding balance. The ear has three main parts: the outer ear, the middle ear and the inner ear.

 Anatomy of the ear

Outer ear

The outer ear includes the pinna and the external ear canal. The pinna acts like a satellite dish that collects sound waves, which are vibrations in the air. The ear canal acts like a funnel. Sound waves travel down the ear canal and cause the eardrum to vibrate. The outer part of the canal is made of cartilage and the rest is bone. The canal is lined with skin. The skin on the outer part of the canal is similar to skin on the rest of the body.

In the ear canal the skin is covered with hairs that help move dirt out of the canal. There are also sweat glands and glands that produce wax (cerumen). The wax is antibacterial and sticky; it assists in waterproofing the canal, preventing small particles from entering the canal, and helps to keep a healthy ear free from infection. In a normal ear the ear canal is separated from the middle ear by the eardrum.

Middle ear

The middle ear is an air-filled cavity, which contains three small bones (the ossicles): the hammer (malleus), anvil (incus) and stirrup (stapes). When the eardrum vibrates the three small bones also vibrate and send vibrations to the inner ear.

The middle ear is connected to the back of the throat and the nose by the Eustachian tube. The Eustachian tube is usually closed but it opens regularly to allow fresh air into the middle ear. This action helps equalise pressure in the middle ear so it is the same as the pressure outside. When people swallow, yawn or sneeze the Eustachian tube opens. The Eustachian tube also helps drain fluids made in the middle ear.

Inner ear

The inner ear is filled with fluid and contains two sensory systems, one for hearing (the cochlea) and one for balance (the vestibular system).
The cochlea is a snail-like structure. Inside the cochlea there are many tiny hair cells that pick up the vibrations of the middle ear bones. The hair cells convert the vibrations into electrical signals which are then transmitted to the brain via the auditory nerve.

The vestibular system consists of three semi-circular canals that assist in balance and help the stabilisation of eye movement.

How do people hear?

Normal hearing occurs when (1) sound waves cause vibrations of the ear drum; (2) these vibrations pass through the middle ear bones (malleus, incus and stapes) to the inner ear; and (3) the cochlea changes the vibrations to electrical messages that are sent to the brain by the auditory nerve.

What is otitis media (OM)?

OM is an inflammation or infection of the middle ear. Otitis means ‘inflammation or infection of the ear' and media means ‘middle'.

What are the different types of OM?

There are different types of OM that represent different stages and severity of the disease.

Acute otitis media (AOM)

AOMViruses and bacteria that cause colds, sore throats and chest infections travel to the middle ear via the Eustachian tube. The Eustachian tube may become inflamed and blocked. White blood cells from the blood help fight infection. After attacking and killing bacteria, white blood cells die and form pus (thick yellowish fluid) in the middle ear. As the infection gets worse, pus builds up and puts pressure on the eardrum causing it to bulge. This stage is referred to as acute otitis media (AOM). This can be painful. However, some children with AOM do not experience ear pain. Signs of AOM include: bulging eardrum, red eardrum, fever, ear pain or irritability.



Otitis media with effusion (OME)

OME

When the Eustachian tube becomes blocked fluid builds up in the middle ear behind the eardrum. At this stage the middle ear may not be infected and the eardrum is intact. This is called otitis media with effusion (OME). ‘Effusion' refers to the flow of fluids from tissue lining the middle ear. A person with fluid in the middle ear may have trouble hearing as the eardrum and the middle ear bones are not able to move normally.




Acute otitis media with perforation (AOMwiP)

AOMwiP

Acute otitis media with perforation (AOMwiP) refers to the stage when the pus in the middle ear first breaks through (perforates) the eardrum. The perforation is usually very small (a pinhole). The perforation can heal and re-perforate. If the infection is not treated properly the hole can get bigger.






Chronic suppurative otitis media (CSOM)

CSOM

When pus continually drains from the middle ear for a long time it is referred to as chronic suppurative otitis media (CSOM), or ‘runny ears'. When the eardrum perforates it no longer moves like an intact drum and patients can experience significant hearing loss. In children with CSOM pus can be episodic (occur only once) or persistent (occur all the time).





Dry perforation

 Dry perforation

When a perforation is dry the eardrum can heal on its own. However, if the perforation is too big the eardrum does not heal. In these cases the ear surgeon can put a patch (graft) over the perforation. In many Indigenous children dry perforations can become reinfected and pus can reappear.






References and further reading

Coates H, Vijayasekaran S, Mackendrick A, Leidwinger L, et al. (2008) Aboriginal ear health manual. Perth, WA:Abbott & Co Printers

Darwin Otitis Guidelines Group (2010) Recommendations for clinical care guidelines on the management of otitis media in Aboriginal and Torres Strait Islander populations. Darwin: Menzies School of Health Research

Images

Chittka L, Brockmann A (2005) Perception of space - the final frontier. PLOS Biology;3(4):(0564-0568)

Hawke M (2004) Hawke Library. Retrieved [date] from http://otitismedia.hawkelibrary.com/normal/Dr_M_Hawke_001

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