Kissiwaa took in the sweet smell of freshly baked bread, so sweet she could almost taste it even as she waited in line to be served. The dry harmattan winds blew against her face amidst the background sound of endless car horns; taxi’s looking for their next passenger. In the space of a few seconds, Kissiwaa had all her five main senses stimulated, providing her with information about the world outside her body. Each of these senses are specialised to a specific part of the body but it is all interpreted by the brain based on electricity. How does the brain do all this? For the first part of this series, we look at how the brain allows us to hear and how it could all go wrong..
The five various organs respond to different stimulus and convert it all into one type of signal which the brain can understand, and that is electricity. Light or sound alongside touch and odours are all converted to electrical signals which the brain interprets to let us see beauty and hear melodies among other things. This contributes to the reason why the brain uses about 25% of energy that the body produces although it makes up only 2% of the body weight.
The auditory system is how the brain allows us to hear
Of all the organs and systems which convert a given sense to electrical signals, the auditory system is one of the most impressive. It converts vibrations in the air, better known as sound into an electrical signal for the brain. Like any finely tuned machine, the auditory system can start to fall apart if abused. This abuse can take many forms but most commonly, it is a prolonged period of loud sound. To understand how this can happen, it is best to appreciate how the system works under normal conditions.
The outer part of the ear known as the pinna, funnels sound in the air towards the ear canal. Once the sound is channelled into the ear canal, it vibrates the ear drum which is connected to three small bones known as the malleus, incus and stapes. These three continue the chain of vibrations which ends in the cochlea. A spiral looking organ where specialised hair cells are attached to a surface which is tuned like a guitar string. Different frequencies of sound cause vibrations in various sections to bend these hair cells; high frequency sounds like that of a whistle vibrate the bottom end while low frequency sounds like a bass drum vibrate the top end.
These hair cells are the pivotal point in the whole auditory system. Each one that bends from vibrations sends a unique electrical signal, the louder the sound, the more they bend, sending a stronger electrical signal to the brain. Once the electrical signal is in the brain, various bits of information are teased out of it to help us identify language, music, tones and so much more.
So how can the whole system go wrong? Well imagine the difference between beating a drum with a small pencil or pounding on it with open palms. That’s the difference between the effects of normal and loud sound. Loud sounds cause strong vibrations which can eventually destroy the hair cells. This primarily leads to hearing loss but can also lead to tinnitus which is the perception of “fake” sounds. .
Tinnitus is the perception of phantom sounds
Tinnitus in particular is an interesting condition because it suggests that somewhere in the brain, a fake signal is being generated in response to a sound which does not exist in the outside world. There are a number of researchers working to understand how this occurs. Their combined findings suggest that after exposure to loud sound, some of the cells in the brain located in an area called the dorsal cochlear nucleus become easily stimulated, making them respond inappropriately to signals. This and other findings could be traced back to the hair cells in the cochlea, suggesting that once these hair cells start taking damage, irrevocable changes follow in the brain.
Some sounds are more dangerous than others
The dangers posed by prolonged exposure to loud sound has been known for a while now. So much so that many countries require by law that people who work under conditions of loud sound have to wear ear protectors. Now isn’t it quite curious that as one group of people are required by law to wear ear protectors, another group willingly expose themselves to the same dangerous levels of sound at parties, events and even through personal headphones. Think of the last time you were at a concert, on a night out or better yet turned up the volume in your head phones while travelling home. The short or long-term damage caused by prolonged exposure to loud sound; whether from headphones or planes remains the same; hearing loss and tinnitus.
