Hearing is the perception that results from our ears transducing sound. Sound is a type of vibration that propagates as pressure waves moving through air or water. Now, waves have what's known as frequency. This is, the cycles per second of a wave. Here you can see a model of a wave, and one cycle would be one complete revolution if you want to think of that, of the wave. So if we start at this point on the wave and go all the way till we get to that same point again, that is one full cycle. Now technically, I should point out that this wave we're looking at here is a different type of wave from a pressure wave. A pressure wave is a longitudinal wave; this is a transverse wave. That's just for the physics people out there. For our purposes, it doesn't really matter because this is actually a much easier visual representation than what a pressure wave looks like. So, just know that one cycle is essentially one revolution of the wave if you want to think of it that way, and that perception of frequency, which is the number of cycles per second, comes in as pitch. That's basically like the notes of music you hear. Right? The different types of sound, the different scales of sound that you hear. That's just our perception of frequency.
Now the amplitude of these waves, which you can see here, this amplitude, is what we hear as volume. So the higher the amplitude of the wave the louder we perceive the sound to be. And our ear is the organ that will take in this sound and turn it into something meaningful for our brains. So, how does that happen? Well, the ear actually has 3 different parts to it: the outer, middle, and inner ear. The outer ear is basically just the cup that sits on the side of our head that is shaped to best gather sound and filter it into this tube. Now, this tube will end at what's called the tympanic membrane, this is the eardrum. It's a thin membrane that separates the outer ear from the inner ear and is going to essentially represent the first step of sound being carried into the body and turned into a meaningful signal.
In the middle ear, we have these bones, and these bones are going to be responsible for amplifying sounds that come from the environment. These bones are called ossicles, and there are actually 3 of them, and you can see them here. We have 1, 2, and 3, and these ossicles will move based on sound waves hitting the tympanic membrane, causing them to move, and basically, they're going to act like a kick pedal on a drum almost, and hammer against this structure, the oval window. Now, the oval window is a membrane-covered opening that leads from the middle ear to the inner ear. So we have these two membrane-covered openings. One that, you know, hits the ossicles and then the one that the ossicles pound on to essentially transmit sound. Now the ossicle that's actually hitting on the oval window is called the stapes. And I also want to briefly mention the Eustachian tube, that's actually what connects your middle ear to your nose and throat region, the nasopharynx. And whenever, if you've ever flown on a plane or had your ears plugged up before, that's from your Eustachian tubes. That's from pressure changes in the Eustachian tubes causing that sensation. So let's actually go ahead and flip the page and move on into the inner ear.