Linda Crampton is a writer and former teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.
The Ear and the Eustachian Tube
An ear consists of far more than the part that we see on the side of our head. It contains three sections—the outer ear (pinna or auricle, ear canal, and eardrum), the middle ear, and the inner ear. The pinna is the part of the ear that's visible from outside the body. It collects sound vibrations and directs them along the ear canal to the eardrum. When the eardrum vibrates, it causes the tiny bones in the middle ear to vibrate as well. The bones transmit the vibrations to the cochlea in the inner ear. The cochlea then sends nerve impulses to the brain, enabling us to hear.
The eustachian tube links the middle ear to the back of the nose. The main function of the tube is to ensure that the air pressure in the middle ear is the same as the pressure in the outer ear and the surrounding atmosphere. It does this by transporting air from the upper throat into the ear. The tube also drains mucus and fluid from the ear.
Unfortunately, a eustachian tube can sometimes become blocked and incapable of transporting substances. As a result, the pressure on the outer ear side of the eardrum may be higher than the pressure on the inner side, causing the sensation of a plugged ear. In addition, mucus and fluid may collect in the middle ear and cause problems.
The information in this article is intended for general interest. Anyone who suspects that they or someone that they care for has a problem in an ear or a eustachian tube should consult a doctor. This is especially important if the problem is severe or persistent.
Multiple names are used for some parts of the ear. In the illustration above, external auditory canal is another name for the ear canal, tympanic membrane is another name for the eardrum, and cochlear nerve is another term for the auditory nerve.
Anatomy of the Outer, Middle, and Inner Ear
The outer ear is made of the pinna or auricle, the ear canal, which is also called the external auditory canal, and the eardrum or tympanic membrane.
The middle ear is filled with air. It contains three tiny bones which are known as ossicles and are attached to each other. These bones are the malleus or hammer, the incus or anvil, and the stapes or stirrup. The stapes is the smallest bone in the human body. It's also known as the stirrup because it looks like the stirrup in which horse riders place their feet.
The inner ear is filled with fluid and contains the cochlea, which is vital for hearing, and the semicircular canals, which are vital for balance. The inner ear, the middle ear, and the ear canal are located in a cavity in the skull.
The vestibular nerve leaves the semicircular canals and the cochlear or auditory nerve leaves the cochlea to carry information from the ear to the brain. The two nerves join to form the vestibulocochlear nerve.
How We Hear
Roles of the Outer and Middle Ear
In order for us to hear, sound vibrations must first travel through the ear canal and then through the tympanic membrane (or eardrum) to the malleus. The malleus transmits the vibrations to the incus and stapes. The three ossicles amplify the sound vibrations, making them about twenty times stronger than they were when they entered the ear. The footplate of the stapes is attached to the oval window, which is covered by a membrane and leads to the vestible of the inner ear.
Role of the Inner Ear
The vibration of the stapes against the oval window causes the window and the fluid in the vestible to vibrate as well. The vibrations are then passed to the fluid inside the cochlea, where they stimulate hair cells. The cells are known as "hair cells" because they have hair-like extensions. They perform a very important job that is essential for hearing. Hair cells convert the mechanical stimulation of vibrations into the electrochemical signals of nerve impulses. The nerve impulses travel along the auditory nerve to the brain. The brain then creates the sensation of sound.
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Eutaschian is pronounced you-STAY-she-un. Most of the time, our Eustachian tubes are closed. When we swallow or yawn, we often hear a clicking sound in our ears. This is produced by the tubes opening up and then closing again.
Functions of the Eustachian or Auditory Tube
The eustachian tube is about 3 to 4 cm long in adults (around 1.2 to 1.6 inches) and is a little shorter in children. It slopes downwards from the middle ear to the nasopharynx, which is the upper part of the throat behind the nose.
The middle ear contains air. The air is constantly being absorbed by the lining of the middle ear, reducing the pressure. Air pressure needs to be the same on each side of the eardrum in order for the eardrum and ossicles to vibrate properly. When a eustachian tube is open, air passes from the back of the nose or throat through the tube to the middle ear, returning the pressure to normal and allowing the eardrum to function normally. The tube also transfers any fluids that build up away from the middle ear.
Children are more likely to develop blocked eustachian tubes than adults. Their tubes are shorter and narrower than those of adults and are also more horizontal, making it harder for fluid to drain out of a eustachian tube into the throat. These factors make it more likely that bacteria and other microbes will collect and multiply inside the tubes. In addition, children have less developed immune systems than adults, making it harder for their bodies to attack bacteria, fungi, and viruses.
The eustachian tubes are named after Bartolomeo Eustachi (also referred to as Bartolomeo Eustachio), a sixteenth century Italian anatomist who was the first person to describe the tubes correctly. Anyone with questions about eustachian tube problems or the other ear problems mentioned below should consult their doctor.
Eustachian Tube Dysfunction or ETD
Eustachian tube dysfunction refers to a condition in which a eustachian tube is blocked, fails to open, or fails to close. If the tube is blocked or doesn't open, the pressure on the outside of the eardrum becomes higher than the pressure on the inside, causing the eardrum to bulge into the middle ear. This process is known as ear barotrauma. Barotrauma is often minor and temporary, but if it's severe or prolonged it may damage the eardrum, reduce the ability to hear, and cause pain.
Any time the pressure is different on each side of the eardrum, a person may feel a fullness in their ears. They may feel like their ears are plugged or clogged. Hearing is often muffled because the eardrum can't vibrate normally. The ears may be painful. There may also be a ringing sound in the ears (tinnitus) or a popping sound. The sense of balance may be affected as well.
A patulous eustachian tube is one that stays open. The condition causes a person to hear normally inaudible sounds created by processes in his or her own body, such as breathing and the heartbeat. In addition, their own voice sounds louder than normal. These effects appear because vibrations in the body travel through the open eustachian tube and strike the eardrum directly.
Possible Causes of Blocked Eustachian Tubes
A mucous membrane lines the inside of the eustachian tubes as well as the middle ear, the sinuses, the nose, and the throat. The membrane produces mucus, which is a thick, lubricating, and protective liquid. A respiratory infection such as a cold or the flu may cause mucous membranes in the area to become inflamed. Symptoms of this inflammation may include swelling of the membranes and excessive mucus production.
Swelling and mucus collection in the eustachian tube can block the passage of air. The mucus may form inside the tube or enter it from another area. A blocked eustachian tube may be unable to open on its own. The condition may be temporary. It may last for a week or more after the respiratory infection has been cured, however, since it takes time for the mucus to leave the tube and any swelling to disappear.
Any allergic response which causes symptoms in the nose, such as hay fever, can also affect the eustachian tube. As in a respiratory infection, inflammation may develop inside the tube and/or in areas around it, accompanied by swelling and increased mucus production.
The lining of the middle ear and eustachian tubes is covered with cilia, tiny hair-like cell extensions that move and create a current of mucus. Smoking can damage the cilia, preventing fluid from being drained from the middle ear. Prolonged and repeated exposure to secondhand smoke can have the same effect.
Other Possible Causes of Plugged Ears
Changing elevation rapidly can alter air pressure in the outer ear. This can cause a plugged ear sensation until the eustachian tube and the lining of the middle ear compensate for the pressure difference between the outer and middle ear. Airplane flights, scuba diving, and driving up or down mountains can all caused plugged ears. If we descend rapidly from a high elevation plane flight, for example, the air pressure in the outer ear becomes temporarily higher than the pressure in the middle ear.
The eustachian tubes may be closed due to the presence of swollen areas nearby, such as enlarged adenoids. The adenoids are clumps of spongy tissue in the nasopharynx near the openings of the tubes. They are largest in young children and shrink with age. Their function is to help fight infection. If they become enlarged, they may close the eustachian tubes.
Injuries that damage the eustachian tube and malformation of the tube can also cause ETD.
What Is Otitis Media?
Otitis media is a middle ear infection and inflammation that is very common in young children. It's much less common in older children and adults, although it does occur in these age groups. In otitis media, fluid collects in the middle ear. The fluid pushes on the eardrum, causing an earache and preventing the eardrum from vibrating properly.
The cause of otitis media is often a problem in the eustachian tube. Infected material from the tube may enter the middle ear, causing inflammation and fluid buildup. The tube normally drains mucus, fluid, and bacteria from the middle ear, but if the tube is infected, inflamed, blocked, or malfunctioning it may not be able to do its job. A collection of mucus and fluid in the ear provides a good medium for the growth of microbes.
Acute otitis media (AOM) may develop quickly, often when a child has a respiratory infection. Microbes can travel from the throat into the eustachian tube and from there into the middle ear. The child may experience ear pain and hearing loss. He or she may sometimes develop a fever as well. The eardrum may break due to the pressure of fluid buildup, releasing pus.
The Nature of Glue Ear
Otitis media with effusion is frequently known as glue ear or OME. It sometimes occurs after AOM but often appears with no obvious cause. In this condition, fluid escapes