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Ears

Lea este articuloListen. Whatever you're hearing — the hum of a computer, your kids playing, a car going by — is thanks to your ears.

Hearing is their main job, but it's not all our ears do. These delicate organs also need care and protection, so let's take a look at how they work and what conditions and problems can affect them.

All About Ears

There's a lot more to an ear than what you see on the side of your head. The ear is made up of three different sections that work together to collect sounds and relay them to the brain: the outer ear, the middle ear, and the inner ear.

ear anatomy illustration

The outer ear, the part that is visible on the side of your head, is called the pinna or auricle. It's made of tough cartilage covered by skin. The pinna's main job is to gather sounds and funnel them to the ear canal, which leads to the middle ear. The pinna, which includes the earlobe, is the part that people pierce to wear earrings.

The ear canal, the hollow passage that leads to the eardrum, is also part of the outer ear. Glands in the skin lining the ear canal produce earwax, which protects the canal by cleaning out dirt and helping to prevent infections.

The middle ear is an air-filled cavity about the size of a pea. It turns sound waves into vibrations and delivers them to the inner ear. The middle ear is separated from the outer ear by the eardrum, or tympanic membrane, a thin, cone-shaped piece of tissue stretched tight across the ear canal.

To hear properly, the pressure on both sides of your eardrum must be equal. When you go up or down in elevation, the air pressure changes and you may feel a popping sensation as your ears adjust. Ears are able to adjust thanks to the narrow Eustachian tube that connects the middle ear to the back of the nose and acts as a sort of pressure valve, opening to keep the pressure equalized on both sides of the eardrum.

The middle ear also includes the three smallest bones in the body, located just past the eardrum and collectively known as the ossicles. The ossicles consist of:

  1. the malleus ("hammer"), which is attached to the eardrum
  2. the incus ("anvil"), which is attached to the malleus
  3. the stapes ("stirrup"), which is attached to the incus and is the smallest bone in the body

The inner ear consists of two tiny organs called the cochlea and the semicircular canals. The snail-shaped cochlea act as a sort of microphone, converting the vibrations from the middle ear into nerve impulses that travel to the brain along the cochlear nerve, also known as the auditory nerve.

The semicircular canals look like three tiny, interconnected tubes sticking out in loops from the top of the cochlea. It's their job to help you balance. The canals are filled with fluid and lined with tiny hairs. When your head moves, the fluid in the canals sloshes around, moving the hairs. The hairs send this position information as impulses through the vestibular nerve to your brain. The brain interprets these impulses and sends messages to the muscles that help keep you balanced.

When you spin around and stop, the reason you feel dizzy is because the fluid in your semicircular canals continues to slosh around for awhile, giving your brain the idea that you're still spinning even when you aren't. When the fluid stops moving, the dizziness goes away.

The cochlear nerve, which is attached to the cochlea and relays sound information to the brain, and the vestibular nerve, which carries balance information from the semicircular canals to the brain, are collectively known as the vestibulocochlear nerve, or 8th cranial nerve.

How We Hear

What's a Sound?

When something vibrates, it makes a sound. Most of the sounds we hear and interpret are vibrations in air (but they can happen in other gases, and in liquids or solids).

When an object or thing vibrates, it flexes in and out. Flexing out pushes the object against the air molecules around it. These molecules in turn push against the molecules next to them. The vibration created travels outward in this manner, much like a ripple or wave. This is a process called compression.

Flexing in while vibrating creates a drop in air pressure that pulls nearby air molecules toward an object. This, in turn, creates another drop in pressure that pulls in the surrounding air molecules, and so on. This process is called rarefaction.

These waves of change in air pressure — compression and rarefaction — are what we hear as sounds.

Detecting Where Sounds Come From

When a sound wave reaches the ear, it's corralled by the pinna and directed into the ear canal. The pinna, through its distinctive shape and curves, helps us determine the direction a sound is coming from. Sounds coming from different places bounce off the pinna differently. The brain can recognize the difference and decide if the sound is coming from in front or behind.

The two pinnae (plural of pinna) of the left and right ears work together to determine if a sound is coming from the right or left. A sound that's coming from the right reaches the right eardrum sooner than the left. It also sounds slightly louder in the right ear. The brain compares the input from both ears and uses this to decide which side the sound came from.

Once inside the ear canal, sound waves vibrate the eardrum, which is very sensitive. The tensor tympani muscle that's attached to the eardrum keeps it taut. So the entire eardrum vibrates no matter where it is hit by a sound wave. This allows the eardrum to detect even the slightest fluctuations in air pressure.

As the eardrum is moved back and forth by the compressions and rarefactions of sound waves, the ossicles move, too. The movement of these tiny bones transmits and amplifies sound waves into the cochlea.

The Ear 'Talks' to the Brain

The cochlea is filled with fluid and contains thousands of tiny fibers that detect sound waves. These fibers are short and stiff in some areas and longer and more flexible in others, which helps each hair detect certain frequencies (pitches).

When sound waves travel into the cochlea, they reach the fibers and give off a burst of energy. This burst of energy is detected by the organ of Corti, a structure that lines the cochlea and contains thousands of tiny hair cells. When energy is released, it's strong enough to move these hairs.

The organ of Corti sends an electrical impulse to the brain telling it which hairs (and how many) were moved. This information helps the brain's cerebral cortex determine the pitch and volume of a sound. So, for example, when a person hears a loud sound, it's because a stronger burst of energy affected more of the hairs in the organ of Corti.

Things That Can Go Wrong With the Ears

Given the outer ear's exposure to the elements and the middle ear's connection to the nose via the Eustachian tube, more than a few things can affect the ear and lead to hearing loss. Fortunately, most of these conditions can be treated effectively when detected early.

Some of the more common ear problems include:

Protecting Your Child's Ears

There's an old saying about how you should never stick anything in your ear except your elbow. It's meant to be funny, but there's a kernel of truth to it. Sticking things like cotton swabs and fingernails into ears can scratch the ear canal, push earwax deeper into the ear, and even rupture the eardrum. If you find yourself having trouble removing earwax from your child's ear canal, seek a doctor's help.

Protecting kids' hearing is mostly a matter of common sense. You can start by convincing your kids to turn down the volume on the stereo and TV and, especially, on portable music players. If you know that they will be exposed to loud noises (at a concert, car race, construction site, etc.), make sure they bring protection for their ears (like earplugs or protective earmuffs/headphones).

If your child has any hearing loss or hearing problems, contact your doctor right away. Depending on the cause, hearing loss can be irreversible. But when treated early, hearing damage often can be minimized.

Reviewed by: Rupal Christine Gupta, MD
Date reviewed: October 2014

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
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