Hearing Facts
Hearing ['hîr-ing]
The sense through which a person or animal is able to perceive sound.
Hearing
Hearing is one of our five senses. Hearing and the other four senses — seeing, tasting, smelling and touching — all play an important part in our understanding of the world around us.
So what is hearing? Hearing is the ability to perceive sound. Your ears are in charge of collecting sounds, processing them, and sending signals about them to your brain. The brain interprets the signals and determines what sounds we're hearing
How Do We Hear?
Hearing happens when the ear changes sound waves into electrical signals that are sent to the brain. We don't really hear with our ears — we hear with our brains!
How the Ear Is Put Together
Let's look at how the ear is put together — scientists call this “Anatomy.” The ear has three main parts: the outer, middle, and inner ear. Here's a detailed, interactive model of the ear's anatomy.
Sound waves enter through the outer ear which is also called the “pinna.” That's the part of the ear that we can see. From here the sound moves through the external auditory canal to the middle ear where they cause the eardrum to vibrate (move back and forth). Another name for the eardrum is “the tympanic membrane.”
The middle ear also has three tiny bones called the ossicles. These three bones are named the malleus, incus, and stapes (and are also known as the hammer, anvil, and stirrup). The eardrum and ossicles make the vibrations larger and carry them to the inner ear.
Fun Fact: Did you know that the frog has an eardrum on the outside of its body behind the eye?
The Cochlea
The cochlea is a snail-shaped, fluid-filled structure in the inner ear. Inside the cochlea are tiny hair-like bundles. As fluid in the cochlea moves against the sensory hairs, the sound vibrations are changed into nerve impulses. These impulses are then sent to the brain along the auditory nerve.
Different sounds move the hair bundles in different ways. This helps the brain to tell one sound from another.
In this photo, the bony wall of the cochlea has been cut away revealing the fluid-filled spiral chambers within. You can see the stapes in the lower left.
The stapes is the smallest bone in the human body. It is only 0.25 to 0.33 cm long [0.10 to 0.13 inches] and weighs only 1.9 to 4.3 milligrams.
Now you are ready to watch this video of how you hear!
Did you know? There are other important structures in the inner ear. They are called the semi-circular canals and they have nothing to do with our hearing. However they are very important for helping us to keep our balance.
Sound Waves
Sound waves have two characteristics that are both important for our hearing: Frequency and Amplitude.
- Frequency determines how low or high a sound appears to us: low like a tuba or high like a flute. Technically, frequency is the number of sound vibrations in a period of time. It is measured in cycles per second (cps), also called Hertz (Hz). Humans can hear sound waves with frequencies between 20 and 20,000 Hz. Some animals, like dogs, bats, and porpoises, can hear sounds at much higher frequencies than humans. Check out the hearing ranges for selected animals. Find hearing ranges for more animals.
- Amplitude is a measure of how big a sound wave is and is expressed in decibels or dB, named after Alexander Graham Bell. Amplitude is the force of sound waves against the eardrum and determines the loudness or volume of a sound. The louder the sounds, the bigger the amplitude of the sound waves, and the more decibels they have.
Learn more at the Science Trek Sound website.
Hearing Loss
Sounds we can hear can be very faint like a whisper (30 dB) to very loud like a siren or jet engine (130 dB). Long exposure to any noise above 90 decibels can cause gradual hearing loss. How does this happen? It has to do with the hair cells. Loud sounds and some infections can cause some of the hair cells to die. Once a hair cell dies it cannot grow back.
We are born with only about 3500 of these hairs, so make sure you protect your hearing from loud noises. You can experiment with sound to see how loud is too loud. Find out if a ringing telephone, a band concert, or an electric drill can impact your hearing with this chart of Environmental Noise Levels.
Examine this list of noises which can damage your hearing. Wear earplugs when you are involved in a loud activity. Learn more about hearing and how to keep your ears healthy.
Fun Links
Hearing
At Neuroscience for Kids you can explore and experiment with your hearing.
Travel Inside the Ear with this video from National Institute on Deafness and Other Communication Disorders.
Step inside the ear in this video from KidsHealth.
In this video from Scholastic, find out how your ears help you keep your balance.
Continue your tour of hearing by trying these online student activities from the National Institutes of Health (NIH), also available in Spanish.
- What Kids Need to Know About Noise and Hearing - Learn how to protect your hearing while still enjoying music and sports events.
- Have You Heard? - Fascinating facts and stories about sounds and hearing
- Listen Up! - How loud is too loud? Find out with this interactive infographic.
What is ear wax for?
Check out the causes of and treatment for Hearing Impairment.
Why is air so important for hearing sound? Find out from Arizona State University.
How Loud Is Too Loud? Take a look at this comic book from the CDC's Ask A Scientist.
Top 10 Questions
February 2007
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Bonus! Can earwigs get into your ears and bore into your brain?
No. Earwax has an agent in it that is toxic to most bugs. Besides, earwax is sticky, so if any bugs do get into your ear, they would get stuck in the outer one-third and wouldn't cause any problems.
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Why do we get dizzy?
There are three parts of our body that help us to know where we are in the world in terms of our balance. One is called our tactile sensation of where we are in the world. Another is vision, where we can see. The third is our inner ear. If we turn our head one direction, the fluid in our inner ear goes the opposite direction. We turn the other way; the fluid turns in the other direction. It lets us know where we are in the world in terms of the horizon. So if there's a problem with that inner ear system, then you'll have dizziness. If you spin around on a Tilt-a-whirl, it can cause residual dizziness. (From Mikayla)
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If you were born without the outer part of your ear, would you still be able to hear?
You can. The outer part of the ear helps funnel sound to make it more easily heard. If the canal, however, is pinched off or if there's bone and no opening to the ear canal, you'll have a greater degree of hearing loss because the sound needs to be loud enough to get through the bone or through the tissue to get to the cochlea. (From Dallas at Gooding Elementary)
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How do you get an ear infection?
When you have fluid in the middle ear space. It should be an air-filled area — if you get fluid in it, because you have a cold and blew your nose and blew stuff up there, it can cause an ear infection because it's a breeding ground for bacteria. Babies seem to get more ear infections because their eustachian tube is almost a straight shot from the back of the throat up, so it's easy for bacteria to be lodged there. (From Reed in Caldwell)
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Can you actually break your eardrum?
Yes, like you can tear your skin, you can break your eardrum. Q-tips can break the eardrum. A blow to the head can cause an eardrum to break. The most common are Q-tips. The old saying is true. Never put anything in your ear except your elbow. (From Conner)
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How do hearing aids help deaf people?
People with hearing loss hear by amplifying the sounds around them. They amplify them differently depending upon whether it's a soft, medium or loud sound or whether it's speech or noise.
There are as many different kinds of hearing aids as there are people. It's important to make sure it's most appropriate for that person's hearing needs. Some hearing aids go behind the ear. Some hearing aids go in the ear. Others have a cochlear implant. A cochlear implant bypasses the outer ear and middle ear altogether.
The success of a hearing aid is dependent upon the individual getting a good test with the hearing aid to decide what's best and also how it should be set. (From Bridger at Pine School) -
Does the eardrum repair itself after getting hurt?
The eardrum is skin. Just like when you have a cut on your hand and your skin will heal, the eardrum also will heal if left alone and left dry. It is able to reknit itself. (From Jacob)
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Why do ears pop?
Ears pop to equalize the pressure. We have air pressure inside our eardrum and atmospheric pressure outside, which is zero. We like those to be equal. If there's a difference we will yawn or open our ears, and that will pop the ears and make the pressure behind the eardrum equal to the pressure outside. (From Summer in Nampa)
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Why are your ears sensitive? How come it hurts with a loud noise?
It's the brain's way of protecting us, like if you stick your finger in your eye and you see sparkly lights. It's your brain's reaction. It's the brain's way of saying, "Let's not go there again." It is like your quick reaction when you touch a hot stove. (From Katie and Tristan in Gooding)
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How loud can you play your headphones and not risk your hearing?
Probably the easiest way to know is — if somebody standing next to you can hear the music, it's too loud. Another way to know is — if you have to raise your voice to be heard from about three feet, then it's too loud and you should turn down the volume. (From Harrison in Mrs. Reeve's 5th grade class at Adams Elementary in Boise)