Introduction

The human ear is indeed one of the most important body senses. It is not only responsible for hearing tones, sounds and voices, but also controls our sense of balance. The ear is the most important tool of communication, because we do pretty much every social interaction throughout speaking. Also we can hear the sound of voices and therefore can decide on whether the other person is angry, sad, jealous or so on. But how exactly does this system work?(1) To answer this question I will cover the different parts of our ear and explain what their contribution to hearing is. Also I will quickly cover the frequency on wich we can hear.

Main Part

How do we hear?

To understand how the human ear works we first need to know out of what parts it consists of. At first we have the outer ear. It is the visible part of our ear and the part wich receives the sound waves and passes them on to the middle ear. In the middle ear different parts, wich I will cover later, start swinging because of the sound waves and transmit those swings to the inner ear. The cochlea, wich is situated in the inner ear receives the sound waves and sets the so called hair cells in motion. The hair cells convert the sound waves in electric nerv impulses. The last in the row is the auditory nerv. The auditory nerv connects the cochlea with the areas of the brain, wich are responsible for hearing. Those areas receive the electric nerv impulses and actually make a tone or word out of it. Now that we have a quick idea of what the inner workings of our ear look like, the different parts will be covered in detail to get a full picture.(2)

The outer ear

The outer ear contains out of the auricle and the external auditory channel. The auricle itself consists of skin covered cartilage. Furthermore there are two big bulges wich give the auricle its characteristic form. The indentations and surveys in the auricle give the incoming sounds, depending on the direction from where they are received, an own timbre with spectral maximums and minimums. Due to this acoustic feature, the localisation of the sound source gets way easier. The auricle also works as a funnel to collect sounds, wich are then send to the middle ear.(3)

(1.1)

The image above shows the outer ear and the external auditory channel.

Middle ear

The middle ear can be divided in multiple parts. At first there is the Tympanic membrane, then the ossicles who border on the oval window and lastly the round window. Everything is situated in the so called Tympanic cavity. There are a few other parts, wich are not important for hearing, and therefore are not covered here. The Tympanic membrane is the border between the external auditory channel and the Tympanic cavity. It mainly consists of tight connective tissue. The Tympanic membrane starts vibrating when sound waves from the outer ear come in. Those vibrations are transferred onto the Tympanic cavity. The Tympanic cavity itself consists out more parts as well, but since they are not involved in the process of hearing, they wont be covered in this article. In the top of the Tympanic cavity are the ossicles, wich are covered with mucous membrane. The osicles can also be divided in three different parts: Malleus, Incus, Stapes. The 3 parts transmit the swinging, that the sound waves bring from ear trumpet, further onto the oval window. This membrane is the border between the middle ear and the inner ear. The oval window finally transmits the swings from the sound waves to the cochlea. The round window is not directly involved into the process of hearing and serves as a vibration compensation.(4)

(2.2)

In the depiction above are not only the different parts of the middle ear, but at the same time the connections to the outer- and the inner ear.

Inner ear

The inner ear again has multiple parts, but only two of them are important for hearing. Those are the cochlea and the auditory nerve. The cochlea is filled with liquid, wich is called perilymph. Additionally it is divided into 3 smaller parts: at first comes the forecourt stairs, second the snail gear and third the timpani staircase. The swings that the cochlea receives from the middle ear are transmitted onto the liquid in the cochlea. Between the snail gear and the timpani staircase sits the basil membrane, wich contains the Corti of organ. The Corti of organ consists out of roughly 25.000 hair cells. The hair cells grab into the tectorial membrane. When the basil membrane gets deflected by swings, the hair cells knick and it emerges an electric impulse. This impulse is then send through the auditory nerve in the brain. But there is another important thing for making out of simple sound wave a tone or word. When the swings have passed the oval window, traveling waves get triggered. They „travel“ trough the complete inner ear into the auditory nerv. With every frequency the cochlea gives a point where the traveling waves have there highest rash. After this the outer hair cells knick hard, wich strengthens the traveling waves and erects the inner hair cells. This erection reaches the auditory nerve and he sends this information to the brain. How the brain makes whole conversations out of just sound waves is an article for itself and therefore wont be covered in this text.(5)

(3.3)

This is one of the best illustrations, to actually illustrate the inner ear. At the left side are the auditory ossicles and the oval window, as well as the round window a little bit deeper. Furthermore is the actual inner ear divided in what is responsible for hearing and what parts are responsible for balance. That is why the upper part with the Vestibular nerve are not covered here. The auditory nerve is missing on this illustration, but it can be dedected as the yellow channel directly under the Vesibular nerve.

The frequency on wich we can hear

The frequency on wich a human can hear differs a little bit. But generally the lowest point on wich a human can hear lays between 0 and 20 hertz. The highest point differs harder and can reach from 16.0000 hertz to 20.000 hertz. The most comfortable range for our ears are frequencies between 500 and 4000 hertz. In this range lays the human voice and usually music. When we talk about decibel, a normal human can hear down to zero decibel. A normal conversation takes place at about 50 decibel and even 120 decibel is fine. But all above this number can cause serious ear damage.(6)

Conclusion

As I realized in the time, where I have written and searched for this text, the human ear is way more complex as I have thought it would be. Beside the three different differnt parts wich are responsible for hearing, there are even more parts in them and even more parts in the small parts. This leads to a situation, where it can be really difficult to unterstand the whole topic, if you are not familiar with the subject. I have tried to only focus on the most important parts and to make them as easy to understand as I possibly could, without taking away to much of the content. To sum it up, I think that the initial question from the whole topic could be answered, beside the complexity of our ear. And I hope that you have now a better understanding of your best communication tool. In my opinion it is a miracle, on how complex our whole body is after countless years of evolution. But at the same time it was really exciting to discover all this unknown parts of this organ. Even though our ear is fully researched, who knows on how advanced we can get in this subject in the future to cure, or at least help out people who deal with deafness or with general problems of hearing.

Sources

Pictures:

(1.1) https://my.clevelandclinic.org/health/diseases/8381-swimmers-ear-otitis-externa

(2.2) https://en.wikipedia.org/wiki/Middle_ear#/media/File:Anatomy_of_the_Human_Ear.svg

(3.3) https://my.clevelandclinic.org/health/body/24048-ear

Text

(1) https://www.einfacher-hoeren.de/de/wie-funktioniert-unser-gehoer__35/

(2) https://www.medel.com/de/about-hearing/how-hearing-works

(3) https://www.tinnitracks.com/de/tinnitus/ohrmuschel

(4) https://www.amplifon.com/de/hoerverlust-erkennen/wie-funktioniert-hoeren/mittelohr

(5) https://www.amplifon.com/de/hoerverlust-erkennen/wie-funktioniert-hoeren/innenohr

(6) https://www.hansaton.at/rund-um-das-gehoer/menschliches-hoervermoegen-im-vergleich/