You step outside early one morning with your coffee. Off in the distance, you hear a bird twittering in a tree across the way. You don’t give this miracle a thought as you take a sip of coffee but you just experienced the miracle or sound. For most of us, sound is just there. All around us. But when you stop for a second to consider the process of hearing, it is, indeed, an amazing journey. Let’s go back to our twittering friend in a distant tree.
Somewhere, far off, a small bird makes a chirp. A short, sharp chirp. That chirp – a sound – creates a disturbance in the air. This disturbance is a series of sound waves travelling, invisibly, through the air. At this point, you still haven’t heard that chirp. The sound waves travel in all directions until some of those waves reach your outer ear – the ear cup, the part of the ear you can see. These outer ear cups are designed to capture that disturbance in the air and direct those sound waves down through the ear canal.
Even at this point, you haven’t heard that twittering sparrow off in the woods.
The Hearing Mechanism
At the end of the ear canal is the tympanic membrane, or what most of us call the ear drum. Here, those delicate disturbances in the air, those sound waves, cause the ear drum to vibrate ever so slightly. But enough to cause the ear drum to vibrate in time with the sound waves. Behind the ear drum are three small bones – the three smallest synapse xt bones in the body. We call them the anvil, the mallet and the stirrup based on their resemblance to these objects. As the ear drum vibrates, it passes these vibrations through the three small bones in the middle ear. These bones, again, vibrate in perfect synchronization with the ear drum. So, that disturbance created by the bird’s twitter has now reached your inner ear as you sip that cup of coffee. Oh, and remember, you still haven’t heard that tweeter tweet.
Translating Sound Waves to Brain Waves
Sound vibrations pass through the three small bones within the ear and reach a snail-shaped organ called the cochlea – the inner ear. The cochlea is filled with fluid and lined with millions of hair-like projections swaying in that cochlear fluid. The three bones transmit the sound vibrations to the cochlea which causes the fluid inside this delicate organ to vibrate. These vibrations are picked up by those hair-like structures and converted to electrical impulses that are then sent to the brain’s hearing centers.
And get this. You still haven’t heard that bird’s distant twitter. But you’re about to.
Once sound waves are converted to vibrations, they’re converted to electrical impulses that are sent to the brain for interpretation. What kind of interpretation? Well, it’s at this stage that you, in your bathrobe, first hear the bird’s tweet – when it’s processed and sent to he brain’s hearing center. Now, the first thing that happens is that your brain goes through its memory bank and “recognizes” the harmless twitter. “Oh, it’s a bird.”
Second, you can place (or localize) the source of the tweet. “It’s coming from that branch of that tree.” That’s because we have two ears. Sound waves reach one ear a little earlier than the other and the brain – a marvel in its own right – interprets the location of the sound’s source. So, once the electrical impulses reach the brain via those hair-like projections in the cochlea, not only do you identify what the sound is, you also determine if there’s danger around you and you position the source of the sound.