Inner Ear, Early Signs of Deafness & Noise Induced Hearing Loss

Why do people go deaf as they age, What's an easy way to detect hearing loss at home & Why do loud sounds cause permanent ear damage?

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All Sound Is vibration

3.2. Photo by Antoni Shkraba

One of the most fascinating facts learnt in elementary physics is how space is mute, soundless and absolutely quiet. This is because sound can’t exist in vacuum. To generate and transmit sound, one needs vibration where one atom hits the other and a wave is formed (impossible in space).

3.3 Getty Images : Creatives commons licence

This wave of vibration passes through air and is picked up by the outer ear. There is subsequent vibration of the ear drum, middle ear cavity and the inner ear.

The Brain is Uni-Lingual

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Our special senses (example vision, taste and hearing) send information to the brain through their respective nerves. However the brain does not understand light, taste or sound. It knows and understands only one language and that is current. If one needs to send information to the brain , it has to be in the language it can understand.

The skin converts the sense of touch to current, the retina at the back of the eye converts light to current, the tongue converts taste to current and the inner ear, specifically the Cochlea converts sound to current.

3.5. Photo by Pixabay, pexels

The Cochlea is a spiral snail shaped structure (Image 3.3). There are small nerve cells (called hair cells) that are spread across the whole length of the cochlea, much in the same way as there are keys on a piano. Just as the type of sound changes when you go from the left to the right on the piano, so does it changes when one goes from the start of the cochlea to the end.

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To understand how sound reaches different parts of the cochlea, one would have to read about the travelling wave theory, the concept of resonant frequencies and other fascinating concepts, but for the sake of simplicity let’s just compare the Cochlea to a Highway and sound vibration to a truck running on it, delivering the right sound at the right place.

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The treble/or high notes are to be delivered right at the beginning of the cochlea. The bass (low frequency sound) needs to travel all the way to the other end of the cochlea, covering the longest distance.

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Which means no matter where the delivery is scheduled, it will go past the beginning . That part of the highway will be used the most because it is Enroute to everywhere else.

No wonder the maximum wear and tear will happen at the the beginning of the highway because of large volume of traffic going through it (basal turn of the cochlea).

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This part of the cochlea is responsible for hearing soft sounds like Ssss, Shhhh, Thh and Ffff. Hence for most people with age related hearing loss, the complaint is not inability to hear but a certain difficulty in understanding speech.

This is because only a part of the cochlea takes the damage. Words like Spark sound like Park, Nest as Net , Bush as Book & Fish as Pitch. This problem manifests especially in a group because in those situations people find it difficult to lip read, plus topics of conversation change frequently making guesswork tricky. The person with a hearing loss makes up for this by frequently asking people to repeat themselves.

Home Testing

The gold standard to diagnose hearing loss is through a test called the Audiogram. Though if one merely has a suspicion, one can do a speech understanding test at home. To do this, stand 6 feet behind the person (so they can't read your lips) and ask them to repeat mono-syllables that you should say very softly. Words like : House , Smile, Graph, Knife, Still, School etc. See how many words out of ten can they get correctly (use words which are familiar to them, example here)

3.10. Excerpt from Maryland CNC word List

If they score less than 70%, you should have them evaluated formally at a medical set up.

Noise Trauma to the Inner Ear

Every road has a weight bearing capacity. If a heavy vehicle with excessive load goes through it, damage will be an obvious outcome. More so when the route is used multiple times.

3.11. Photo by Songhan Wu

Likewise, very loud sounds transmit a lot of energy to the inner ear which vibrates the system beyond its limits of elasticity, thus causing permanent damage to the small hair cells. There are international guideline that suggests safe hearing levels for individuals to prevent permanent damage to the hearing. Sounds below 80 dB are considered safe, while those above that can cause damage based on the duration of exposure. In a nutshell, green is good, while orange and red requires hearing protection to prevent Noise Induced Hearing Loss.

3.12. Image from UK Hearing Conservation Association