Table of Contents
Mechanisms of sound perception
From a Stravinsky’s composition, to the laughter of a baby or a smoke alarm in a building… The variety of sounds that humans can perceive is enormous and it is possible thanks to our sense of hearing. This sense is just as complex as the other four and it allows us to perceive sound through a specialized network of neuronal connections that go from our internal ear to the brain. But, how does sound travel inside our ears? Let’s find out.
The auditory system: The outer ear
The auditory system is composed by the outer, the middle and the inner ear. The outer ear includes the auricle and the ear canal. The auricle is made of cartilage, which is a soft tissue that can maintain a certain shape but is still very flexible.
Without the auricle, we will certainly look as aliens, but it would also be very difficult for sound waves to get into the ear canal. There is a difference between the external pressure and the pressure inside the ear. If sound vibrations reached the ear directly, they would literally face a counter pressure force that would make most of them to get lost and the others to enter abruptly into the ear canal.
The eardrum, which is located at the end of the ear canal, is an essential part if the outer ear. Also known as tympanic membrane, it is a very thin membrane that is well protected both by the shape of the ear canal and the earwax in it, but it can be easily damaged. Eardrum rupture can happen even by just a change of pressure, when swimming, for example. This rupture can be easily treated, but it has to be done right away in order to avoid more pain and possible bacterial infections, as well as a more permanent damage to the ear structures and function.
The middle ear
Three tiny bones are located in the middle ear: the hammer, the anvil and the stirrup. The eardrum vibrates when it receives the sound vibrations coming from outside, through the ear canal.
When this happens, vibrations created on the eardrum pass through the hammer and the anvil first, and finally to the stirrup. The stirrup sends them onto the oval window.
The journey that sound makes from the eardrum to the oval window has an amplifying effect on it.
The Eustachian tube runs from the middle ear to the rearmost part of the palate. Why? Its job is to keep equilibrium in air pressures in both sides of the eardrum.
Sometimes, this does not happen, and the ear feels as if it was blocked by something that is not allowing sound to travel through. You just have swallow a bit of saliva and the Eustachian tube will open to balance pressures again.