Charting the ear's geography


Ears come in all shapes and sizes, but they all serve as a way to collect vibrations known as sound waves, processing them and sending information to the brain for interpretation.

In humans, sound travels through a fleshy exterior into a middle chamber containing three highly functional bones, and then to an inner ear chamber, which uses fluid to pass on information channeled from nerves to the brain.

"The way sound travels, it goes through a process from mechanical to fluid to nerve to electrical impulse. It's a really complex system," said Glen Datres, a doctor of audiology, also known as an audiologist, who works at Barrington Audiology in Great Barrington.

There are three main parts of the ear: outer, middle and inner.

The outer ear is visible on a person, and is known as the pinna, auricle or auricula. Its main function is to collect sounds. In humans, the outer ear begins developing around the fifth week of pregnancy.

Different diagrams can give up to a dozen names for the different ridges, folds and indentations that shape the outer ear. The basic anatomy of this single piece includes the top ridge or helix, a ridge closer to the center known as the antihelix, and the earlobe, also known as lobule or auricle. The pinna is flesh-covered cartilage, which people commonly pierce for wearing jewelry. Piercings must be carefully made and regularly cleaned and cared for to prevent infection and deformities.

Also part of the outer ear is the ear canal, which funnels sound inside the head toward the middle ear. In formal terms, it can also be called the external auditory meatus or external acoustic meatus. Glands in the skin lining the ear canal are what produce earwax, a natural compound produced by the body to clean and protect the canal from infections.

Though earwax is, by design, a self-managing substance, there are a number of products, from ear vacuums to cotton swabs, which people tend to use to clear the wax. In general, Datres warns against using these products, because they could end up causing more damage.

"In theory, [wax] is meant to handle itself," Datres said.

He said that using swabs can dry out the walls of the ear canal or push wax against the ear drum, part of the middle ear. He said other methods, including one known as ear candling, can be both dangerous and ineffective.

Datres said the shape of each person's ears are "pretty darn unique." He said with some people, a light can be directed into the canal, and, using a medical device called an otoscope, the viewer can see straight through to the ear drum. With others' ears, the light may have to travel down a more narrowed canal or one that curves and obstructs such a view of the middle ear.

The middle ear itself contains the tympanic membrane, or eardrum. It's a thin, slightly cone-shaped piece of tissue that stretches tightly across the ear canal and converts sound waves into vibrations that travel into the inner ear.

The eardrum is surrounded by a sort of pressurized cabin, a hollow air-filled cavity that helps balance the sound we hear. When the pressure changes, such as when we are hiking at a high altitude, flying in an airplane, or on an amusement park ride, ears may "pop" as a mechanism of adjusting. The anatomy in the middle air that helps to equalize the pressure is called the Eustachian tube, which connects to the back of your nose.

When we are children, the Eustachian tube has a more horizontal alignment, and it becomes more vertical as we grow into adults. The horizontal alignment means that more bacteria can travel from the nose to the ears, which is why children are often prone to ear infections.

The eardrum also acts as a divider between the outer ear and the portion of the middle ear that contains the ossicles, a trio of tiny and delicate bones known as the malleus (hammer), incus (anvil) and stapes (stirrup). They are attached to each other in that order, so when the sound waves reach and vibrate the eardrum, it moves through these bones which connect to the inner ear.

When it is vibrated, the stapes stimulates a snail-shaped organ called the cochlea, which is encased in bone. Sticking out in loops at the top of the cochlea are the semicircular canals. These tiny organs are filled with fluid and highly sensitive hair cells that, based on vibrations and motion, send messages as impulse from the moving fluid, which in turn bends the hair cells. Like a wave, the message is passed through the attached auditory nerve to the brain. Impulses from the cochlea help the brain interpret sound, while impulses from the semicircular canals help the brain communicate with muscles to keep a sense of balance.

Datres said factors such as hereditary conditions, age, poor development, diet, lifestyle, loud noise and/or consistent and prolonged exposure to noise can affect people's abilities to hear. Generally speaking, it is the nature of the hair cells in the inner ear to age with us. They can become atrophied or can actually burst by exposure to a sudden loud noise. They also have the elasticity to grow back. Other problems such as swimmer's ear (a fungal infection in the outer ear), which can affect hearing, are also treatable. Damage to the auditory nerve itself is much rarer.

"We always encourage people if they start to experience some part of hearing loss to get checked immediately. Some people wait, but the sooner you get treated, the better your brain will adjust to the changes," Datres said.


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