Can you hear that?
Boring Saturday night: staying home, watching the football match on TV (Italy v. Ukraine, I think) and trying to kill my headache.
Journalists are on strike here, so, the match is broadcasted without anyone telling exactly what you are seeing or giving you priceless information about players' nicknames.
This afternoon I studied how our auditory system works.
I find interesting the difference between sound wave and sound. Our brain detects the former, while sound should be defined as the perception of amplitude, frequency and complexity of the wave.
To sum up, there is no sound without a centrel nervous system interpreting it. No music, no word, nothing.
Basically, the auditory system can be divided in three parts: ear, auditory nerve pathway and central auditory system.
Ear is composed by outer, middle and inner ear. Pinna and ear canal help sound waves to reach the inner parts. Then, these waves of pressure become liquid wave: the tympanum vibrates and, thanks to malleus, incus, and stapes, the stimulus is amplified.
Another membrane, called the oval window, allow the mechanical vibration to reach the cochlea, which is located in the labyrinth. Here is situated the organ of Corti: on top of it, there is a membrane, whose vibration moves hair cells.
These hair cells present mechanically gated ion channels: when they move, more potassium and calcium ions enter, resulting in a depolarization. This increases the quantity of neurotransmitters released, which react with the receptors on the membrane of primary sensory neurons (the ratio is 1:1).
Now, the mechanical stimulus has been converted into potential energy, which is carried by the vestibulocochlear nerve, until the left cochlear nucleus. Next step is the superior olive: from now on, the information goes to both brains (left and right, which has led to two theories that try to explain how we can understand where the sound came from).
Then, the message reaches the right inferior colliculus and, subsequently, medial geniculate nucleus.
The final step of this pathway is the temporal lobe, where, in the superior temporal gyrus, the primary auditory cortex is.
Frequency is determined by the position of the activated receptors: the closer to the oval window, the higher the frequency.
Amplitude by the amount of neurotransmitters. Complexity is analyzed by some of the cells of the primary auditory cortex, which have solely this task.
Oh, well, I've just realised, once again, I haven't talked about chemistry, but looking at the latest Nobel prize for chemistry...I'm probably on the right track for a successful career, eh?
