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The Sound Of Music: How Do We Perceive Sound?

by — 2014-09-11 in Ear, Nose, Throat, and Dental problems
The five senses are sometimes taken for granted. We use them all the time, for every single activity we perform and still don't know much about them. Here's an overview of how our ears work in order to receive sound and send it to the brain for coding.

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.

The outer ear works as a sound collector; apart from protecting both the middle and the inner ear, the shape of the auricle, which is pretty weird if you ask me, is specially designed to capture sound vibrations, gather them and help them travel into the ear canal.

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 auricle smoothens the journey of the sound vibrations from the outside into the ear canal and further down.

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.

Read More: Imbalance and Dizziness caused by Superior Canal Dehiscence Syndrome

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.

Every time you swallow, the tube opens and equalizes air pressure.

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.  


Continuing The Journey: The Inner Ear

Sound has finally reached the inner ear, after a long but very fast journey. Here we can find the organs that are in charge of sensing sound vibrations but also of maintaining balance. The cochlea is one of them. It is a bone with the shape of a snail and it is filled with fluid. Inside the cochlea, there is a group of specialized cells, known as hair cells that will send the sound signals up to the brain.


From vibrations to electric impulses

But, until this point, are sound vibrations still vibrations? Let’s summarize until here: sound, in the form of vibrations, reaches the eardrum. The eardrum sends them on to the three tiny bones, which move and transmit this movement on to the oval window, by pushing it. This push makes the liquid inside the cochlea to also move and stimulate the hair cells that sit there. Hair cells are nervous cells that connect the ear to the brain and basically take the sound stimuli up to the brain region that is in charge of coding it.

Hair cells are very special. They can look very similar to each other, but are actually different.
Each one of them responds to a different sound pitch, so depending on the frequency of the vibrations, some cells are stimulated and some others are not.

Hair cells send these stimuli in the form of nerve impulses through the auditory nerve. The nerve reaches the auditory region, which is located in the temporal lobe. The temporal lobes are the ones that are on the sides of the brain, just by where your ears are located.

Hearing loss

Hearing loss can be caused by a variety of factors and it can be mild or severe, depending on the cause. For example, it can be due to a blockage of the ear canal caused by earwax or an object. In this case, the removal of the foreign object will bring everything back to normal, without any further consequences other than maybe some inflammation and mild pain. Sometimes it is not this simple.

Hear loss can be also caused by the death of hair cells, cochlear damage and alterations in the nerves that connect the inner ear to the brain.

This happens normally as part of the aging process, but it can also be a consequence of a hereditary disease, head trauma, illnesses, some drugs and exposure to loud noise.

Ear care and disease

Our ears need be taken care of. To clean them, just wipe the outer ear with a clean cloth; never use Q-tips, bobby pins or any other object to clean your ears, because this might cause you to break your eardrum.

Follow the saying “never put anything bigger than your elbow inside your ears”.

See Also: Bulb Syringes Are an Effective Tool for Earwax Removal

Even when it is a bit disgusting, earwax is there to protect your ears, but sometimes it can build up and block them. Don’t attempt to remove it by yourself, it is better if you ask your doctor to examine your ears and help you with this problem. Ear infections are common, especially as an effect of respiratory diseases, but you can prevent them by treating any respiratory symptom as soon as possible. Noise and loud sounds can severely affect your hair cells in the inner ear. To keep them alive and functional, try to avoid exposure to loud levels of noise by using earplugs or other proper protection and avoid listening to music in loud volume.

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