After reading WONDERSTRUCK, your kids may be thinking more about hearing. It’s not hard to understand how hearing works–it’s actually very mechanical. Vibrations are passed along a chain of structures, translated into electrical impulses, and sent to the brain to be interpreted as sound. But, the complexity of these mechanics–the intricacies necessary to make it all happen–has many vulnerabilities. Even a small breakdown in the system can leave a person with hearing challenges, like WONDERSTRUCK’s main characters, Rose and Ben.

HOW SOUND STARTS

First, to understand hearing, we must understand a little about sound. Sound is created through vibrations–banging a drum vibrates the drum head, clapping our hands vibrates our flesh. These vibrations in turn create waves of vibrations in the molecules of the surrounding matter, usually air. (How well these vibrations travel depends in part on how tightly the molecules are packed together, explaining why tapping on a wooden or metal table will sound so much louder when you put your ear to the solid surface than when you listen to it through the air.)

THE OUTER EAR–COLLECTING THE WAVES

These vibrations travel to our ear and are collected and funneled inward by the part of our ear that we can see, called the auricle or pinna. The pinna’s shape is specially designed to collect sound waves and direct them into our ear or auditory canal, which also helps condense the waves as they get closer to our eardrum.

THE MIDDLE EAR–TRANSMITTING THE VIBRATIONS

Our eardrum, also called the tympanic membrane, is aptly named because it is like a drum head–elastic and stretched tight in order to be easily vibrated by even the tiniest wave. The tympanic membrane also serves to separate the outer ear from the more vulnerable and delicate structures in the middle and inner ear, preventing foreign bodies from entering. The eardrum then acts as the intermediary between sound creation and sound interpretation, in that it is the eardrum vibrating that, in turn, vibrates the tiny bones called the ossicles in the middle ear.

The ossicles are three bones in the middle ear, named based on their shapes. Attached to the inside of the tympanic membrane is the malleus (or “hammer”), which is connected to the incus (or “anvil”), which is connected to the stapes (or “stirrup”). When the eardrum vibrates, it moves this chain of tiny bones. They, in turn, are connected to another very important structure in the inner ear called the cochlea, where vibrations are finally turned into a stimuli our brains can interpret–electrical impulses!

THE INNER EAR–TRANSLATING TO THE BRAIN

The cochlea is like a tube, coiled up into a snail-shaped spiral, and lined with cells covered in tiny hairs floating in fluid. When the stapes (the final of the three ossicles) vibrates, it vibrates the cochlea via the “oval window” which is the point where the two structures are attached. When the cochlea receives the vibrations from the stapes, the fluid inside conducts the vibration and moves the tiny hairs lining the cochlea’s inner surface. These amazing little hairs communicate with the cells they are attached to, which then create specific electrical impulses based on their movement. The cochlea finally sends these impulses to the auditory center of the brain via the auditory nerve, where the brain interprets it as sound!

• Here is a short (1:44) animation about hearing.
• Ear anatomy diagram printable worksheet with key
• At KidsHealth.org, you can explore more about hearing, take a quiz, and print an ear anatomy diagram.

SIMPLE EXPERIMENT–MODEL EARDRUM!

Create a model to show how sound waves travel and cause the eardrum to vibrate! You’ll need:
large potpiece of plastic wrap to cover the top of the pot very tightly (if your plastic wrap won’t hold, use a large rubber band around the top to pull and hold it tight)a few grains of rice, tiny pebbles, or sandcookie sheetwooden or plastic cooking spoon

1. Stretch the plastic tight over the top of the pot and secure. Place the grains of rice or pebbles in the center of the plastic wrap. Stand near the pan with the cookie sheet and the spoon. Keep the kids nearby so they can see the rice, but warn them to plug their ears!

2. Holding the cookie sheet near the pan, bang it with the spoon and watch the rice vibrate!!

What’s happening? The sound waves created by banging the pan are traveling through the air and vibrating the plastic wrap, just as sound waves vibrate the eardrum. Try a variation–loosen the plastic wrap and try banging the cookie sheet again and see if the rice moves less, just like the eardrum is less able to conduct sound waves if it is ruptured or perforated!

~Michelle

image credit: Wikipedia