Senses Primer Part 2: Hearing

I love music. I would pay spotify 100 dollars a month for premium if I needed to. That’s more than what I would pay for health insurance. Music is my personal conduit for emotions, but more importantly, it’s only possible because I have the ability to hear.

 

Hearing is the ability to detect sound waves. Sound waves are vibrations through a medium, usually air. Usually, only pitch and loudness are the interesting parts of sound waves. When these vibrations happen, our ears pick up on these vibrations, and convert these vibrations into electrical signals sent to the brain.

 


 

The ear is separated into three parts: the outer ear, the middle ear, and the inner ear. The outer ear’s job is to detect the vibration through an ear drum. When that drum is vibrated by sound, it moves bones in the middle ear. These bones push towards fluid in the inner ear, and the inner ear converts the movement of fluid into electrical signals.

 

The outer ear is the easiest and most intuitive to understand. Imagine a cone with a condom put on the smaller end of the loud-speaker. A cone shape captures a lot of sound, and the sound is redirected towards the condom. When the sound waves hit the condom, the condom vibrates. This is what your eardrum does. The job of the outer ear is to capture sound, and get it to hit your eardrum (which is part of your middle ear, but I feel that it’s easier to explain it this way).

 

 

When your eardrum vibrates, it sets off the movement of bones in your middle ear. The malleus, which is a bone attached to the eardrum, starts moving and hitting the incus (the names of these two bones are hammer and anvil because of this). The incus starts to move the stapes, another bone, when banged on by the malleus. The stapes, which means stirrup due to its shape, is kind of like a plunger that pushes fluid in the inner ear.

 

 

The inner ear is the weirdest part of the ear. Just look at that alien structure. Anyways, the inner ear is also responsible for balance as well as hearing, so let’s try to dissect the inner ear more. The part of the inner ear responsible for hearing is the cochlea

 

The cochlea is a spiral shaped organ. This spiral shape matters, because at different parts of the spiral, the cochlea is stiffer. What ends up happening is that different parts of the cochlea will activate more or less, depending on the pitch of the sound wave. This is how your ears distinguish between a low note and a high note.

 

 

At each part of the cochlea, little hair cells exist that will move up and down because of the waves created by the stapes pushing on the fluid. This up and down motion activates these cells, and these cells will send signals to your brain. The more extreme the up and down motion, the higher the volume.

 

 

Hair cells are kind of weird too, and they also require a little background knowledge to understand perfectly. Boiling it down, the up and down motion of the hair cells causes little channels on the surface of these hair cells to open. When these channels open, potassium enters the hair cell. When enough potassium enters the hair cell, calcium will also enter the hair cell. When enough calcium enters the hair cell, a signal is sent from the hair cell to the brain. When you have enough of these signals happening, you get sound, speech, and music.

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