by Thomas Tagoe, Accra College of Medicine, @Tom_DAT
Benedicta took in the sweet smell of flowers in the field as she felt the chill of a cool breeze blowing over her. She could hear the sound of rushing waters from the stream nearby as she lay in the grass biting into a freshly baked doughnut and marvelling at the birds flying high over-head.
In the space of a few seconds, Benedicta had all her five main senses stimulated, providing her with information about the world outside her body. Each of these senses is specialised to a specific part of the body; nose to smell and skin to touch, eyes to sight, ears to hearing, and tongue to taste. Although each of these senses is assigned to a specialised part of the body, it is all interpreted by one part of the body: the brain.
The five organs respond to different stimuli and convert it all into one type of signal, electricity, which the brain can understand. Light, sound, touch, and odours are all converted to electrical signals which the brain interprets to let us see beauty, hear melodies, and experience the world. This is part of why the brain uses 25% of the body’s energy although it makes up only 2% of the body weight.
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, such as through exposure to prolonged periods 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. This is the reason cupping your hands behind your ears makes hearing better. 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 much more.
So how can the whole system go wrong? Imagine the difference between beating a drum with open palms and pounding on it with clenched fists; 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, the perception of sound in the absence of an external stimulus, typically experienced as a “ringing in the ears”.
Tinnitus is an interesting condition because it suggests that somewhere in the brain, a false 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 findings suggest that after exposure to loud sound, some of the cells in the brain 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 get damaged, irrevocable changes follow in the brain.
The dangers posed by prolonged exposure to loud sound have been known for a while now. So much so that many countries require by law that people who work under conditions of loud sound wear ear protection. Now isn’t it quite curious that as one group of people are required by law to wear ear protectors, while another group willingly expose themselves to the same dangerous levels of sound. 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.