Imagine it is your job to create a system to allow humans to detect sound. You are the person in charge of developing the auditory system (aka hearing!). Go!
Yup pretty much. Sounds difficult eh? Well good thing for you I'm here to help.
You would probably want to develop cells in the ear that detect sound- good place to start right?
You would have some cells detect different sounds too, right? What we call 'sounds' are simply differences in frequency- known by the lay person as 'pitch'. High pitch sounds are high frequencies and low pitch sounds are low frequencies. So, you would probably want different cells that are able to detect different frequencies.
Let's say you developed the auditory cells to hear frequencies from 200-800 hertz (hz)- which is actually the true case in humans- we hear sounds from about 200 to about 800 hz. Don't waste time developing one cell for 200 hz and another 201 hz- there is an immeasurable difference between the two! It would be a good idea to have some for 200 and some for 300, and for 400, etc. This way, when the one for 300 is fully activated, and the one for 200 is activated just a little bit, you know that you have 290 hz...and the same thing for the 300 and 400 cells if you had 310. Follow? In fact this is a simple version of how the human auditory system works...but here's where it gets tricky.
So, you have all of your cells that can detect specific frequencies of sound and, depending on how many are activated, etc, you can hear many different sounds. All is good in the world of hearing. Now we have to get this sound detection to the brain. Let's say we played a sound a sound at 300 hz over, and over, and over again. What would you want the brain to recieve as a message? I'm assuming you want the brain to recieve the exact same message every time a 300 hz sound is played, right? Makes sense...but apparently God (perhaps using his developmental tool of evolution) doesn't think this way. No- He decided that our auditory cells should send different messages to the brain each time it hears the same sound. This is explained in more detail below, but the cells respond either strongly or weakly, almost at random.
There is an average neuronal depolarization of about 33 millivolts each time a 300 hz sound is detected by the mammilian brain. This is an average...it could be 30, or 28, perhaps 51 or as high as 60. They will average to 33...but no one knows why it isn't 33 all the time.
Any thoughts as to why this would be? There are no known temporal or spatial mathematical relationships...try to think outside the box on this one.