Science for Kids - Hear! Here!

By: Tracy

If Shakespeare had asked ‘What’s in an ear?’ he may have been surprised by the answer. And so might your child! There are lots of things in the human ear. There are tools – hammers and things – mazes as well as tubes and canals. You will find air and fluid, hair, nerves and organs. All of that packed into a tiny space between the outside of your head and the inside of your skull. And what’s it all for? A healthy set of ears will help us hear all the wonderful things that are going on around us. We can hear birds singing, cars humming and the shouts of ‘Mom, I don’t wanna wash my hands!’ by those we love.

The next time your child bellows out with his/her outside voice in the house, why not use the moment to start a lesson on the ear and how we hear? Give your kid’s
pinna – the visible portion of the outer ear that focuses sound waves – a gentle tug and tell him/her that all the yelling is vibrating your ossicles. Now that you’ve got their attention, you can use the following fun facts to teach your kids about their ears:

Fun Facts about Hearing – For kids

Our ears are divided into three sections; the outer ear, the middle ear and the inner ear.

The outer ear is made up of the pinna – also called auricle – and the ear canal. Humans also have earlobes which, besides being a good place to put earrings, serve no real function. Other animals don’t even have them.

Many animals can move their pinnae in the direction of the sound they are trying to listen to. Watch your dog or cat when they are trying to listen for something – can you see what their pinnae are doing? They are moving back and forth trying to pick up the sound. Human ears don’t have the ability to do this. We have to turn our heads to help us pick up sounds more effectively.

Sound travels in waves that move in many different frequencies – this means the wave goes up and down a certain number of times in a second. Sound waves are named for their frequency number and this measurement is given in a unit called Hertz (Hz). Humans hear frequencies that range from 20-20 000 Hz. That’s a big range, but some animals can hear frequencies that are higher than this number – these are known as ultrasonic frequencies. Some bats and all dogs can hear ultrasonic frequencies that we cannot. This is why dog whistles have been invented; these whistles will attract dogs without being heard, at all, by people.

The ear canal ends in the tympanum or ear drum. This is not a drum you hit with sticks but it does get hit with sound waves coming down the ear canal.

The middle ear is made up of the ear drum and the ossicles. The ossicles are three tiny bones with funny names. The first is called the hammer, the second is the anvil and the third is the stirrup. These three bones aren’t actually used like the tools that they are named for. They are named this way because they are found to be the same shape as these tools; the hammer is shaped like¼well, a hammer, the anvil like an anvil and the stirrup like that metal thing you put your foot into when you’re riding a horse. The real names for these bones are in Latin: they are the malleus, the incus and the stapes, respectively.

The ear drum actually touches the first of the ossicles – the hammer – and turns the vibrations of air waves in the ear canal into vibrations on the hammer. The hammer touches the anvil and the anvil is connected to the stirrup and so, once the hammer is vibrating away, it will get the other two bones going as well. The last bone, the stirrup, lies up against the next part of the ear; think of these little bones as the TOOLS that get the rest of the ear apparatus vibrating.

The middle ear is hollow and full of air.

The inner ear is made up of the oval window, the snail-shaped cochlea and the maze-like labyrinth that we use for balance.

The inner ear is full of a fluid called endolymph.

Vibrations are transmitted through this endolymph. To get an idea of how this may work, fill a bucket with water. Tap on one side of the bucket and watch how your tapping vibrates the water inside. You’ll notice that the waves go from the side of the bucket where you tapped, right over to the other side of the bucket. This is pretty much how sound waves travel through the endolymph in the inner ear structures.

After the sound vibrations have been transmitted to the oval window by the ossicles, they move on to the snail-shaped cochlea. Inside the cochlea is a thin skin-like surface, or membrane, called the basilar membrane. This membrane has another membrane sitting on top of it – the Organ of Corti - that has hair-like protrusions on it called hair-cells. Here is what happens: Different frequencies get different parts of the basilar membrane vibrating and this gets the Organ of Corti membrane on top of it shaking away as well. The hair cells on top of the Organ of Corti will then be rattled as well and these will start to send messages to the nerve that travels to the brain.

The hearing nerve that travels from the ear to the brain is called the auditory nerve. It is also called the cochlear nerve because it comes off of the cochlea.

Very loud noises will cause very strong movements of the hair cells. If this goes on for too long, these hair cells will die and your hearing will get worse. So, we want to protect those hair cells as much as we can¼let’s keep that TV volume down!

The other part of the inner ear is the labyrinth. This is a maze of canals called the semicircular canals. This part of the inner ear does not deal with sound waves but detects rotation of your head. Every time you turn your head, the fluid – endolymph – in the inner ear swishes around in the direction of the turn. This keeps you from losing your balance. If your labyrinth were not working properly, you would get dizzy and, possibly fall over, every time you turned your head!

There are tubes, that come off of each of your middle ears, called the Eustachian tubes. These go to the inside of your nose. Their purpose is to keep the pressure in your ears steady. This pressure can change if you go underwater or if you’re very high up in the sky – such as in a plane. If the pressure in your air-filled middle ear gets to high, your ear drum may burst and then your ability to hear will be reduced severely.

Your Eustachian tubes are pinched off inside your nose so you won’t get mucous in them and prevent them from working. (Mucous, you might have to explain to younger children, is the stuff that comes out when they blow their noses.) To open them, you can open your mouth to lower your jaw bone. This is a common thing for people to do in a plane as they are getting accustomed to the pressure changes while the plane goes higher and higher.

Even though it’s a common practice, you really should not clean your ears with a Q-tip. If a Q-tip gets shoved too far into your ear, it may go through your ear drum and severely compromise your hearing. Your doctor will tell you: don’t put anything smaller than your elbow into your ear!

There are lots of things you can teach your children about their ears and how they hear. This can be a long lesson, so spread it out over time; when they yell, when they spin around and around so much they lose their balance, when they’re going swimming and go underwater¼even if they’re playing with toy tools, you can always sneak in a comment about the hammer they have in their ears!

Shakespeare would have been impressed if someone had told him, ‘what’s in an ear!’ Your kids will be too!

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