The ear consists of the outer, the middle and the inner ear. Each part of the ear plays an important role in catching, directing and transmitting sound. The ear is also important for our balance and maintaining our body position. Sounds that exceed 85 decibels might damage hearing and sometimes even cause irreparable hearing loss. In order to understand why and how this happens, it’s important to be familiar with the structure and the function of the ear.
The outer ear is the part most people refer to when they talk about ears. It’s made of the pinna, the muscles of the outer ear and the ear canal. The length of the ear canal is about 2 and a half centimetres but its size and shape varies. The ear canal amplifies sound waves before they are transmitted to the middle ear.
The middle ear consists of the tympanic cavity, the ossicles and the muscles of the middle ear. The tympanic cavity is the hollow space in the middle ear. The ossicles are the small bones of the middle ear – they are known as the hammer, the anvil and the stirrup (because of their distinct shapes). Their role is to transfer sound vibrations into waves in the fluid and membranes of the inner ear. As the sound enters the ear, it vibrates the tympanic membrane (commonly known as the eardrum). The hammer is attached to the eardrum and it moves when the eardrum starts to vibrate. The hammer transmits the vibrations to the anvil and finally to the stirrup, which transfers them to the inner ear.
The inner ear is the part that is responsible for balance and sound detection. It consists of the cochlea and the vestibular system. The cochlea enables hearing – when the stirrup presses against the oval window (the beginning of the inner ear), it transfers the signals into waves in the fluid and the membrane of the middle ear and these waves stimulate hair cells in the inner ear. Each of these hair cells responds to a specific frequency. The signals are then transformed into nerve impulses that travel to the brain, which interprets them.
The vestibular system is important for our balance – it uses the same type of fluid and cells as the cochlea, but they have a different function. They send information about the linear motion, rotation and attitude of the head to the brain.
What happens when the sounds are too loud?
Noise induced hearing loss (NIHL) (also referred as industrial deafness or occupational deafness) can be caused by one time intense “impulse” sound (explosion) or by continuous exposure to loud sounds over extended periods of time (workplace noise). Some recreational activities can also damage hearing – listening to loud music through earphones, loud concerts or playing in a band can potentially damage your hearing as well.
Long/repeated exposure to loud sounds (sounds above 85 decibels) can cause hearing loss. For instance – heavy city traffic has an average decibel rating of 85. Normal conversation usually doesn’t have more than 60 decibels. MP3 players at their loudest can produce sounds as loud as 105 decibels, while sirens produce 120 decibels and firearms and pyrotechnic devices go as high as 150 decibels. Prolonged exposure to high decibel levels in the workplace have given rise to a claims for occupational deafness compensation.
The hair cells in the inner ear that detect certain frequencies can be irreparably damaged by loud sounds and they lose their ability to detect frequencies, which means they can’t detect sounds anymore. Human hair cells don’t grow back – once they are gone, they are gone for good.