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Hearing Loss - How We Hear
By Val Bedard

Hearing is a complicated process involving both the sensitivity of your ear as well as the ability to hear and understand speech. Speech includes a combination of low and high frequencies. Depending on where your hearing loss is, that will be where you will experience difficulties.

When we hear correctly, the brain has interpreted the signals brought by the ear, through the canal, through the cochlea and then to the nerves leading to the brain. When something is not working properly along this sophisticated chain, the brain misinterprets and you do not understand.

Hearing occurs when sound waves reach the structures inside your ear, and your ear converts the sound wave vibrations into nerve signals that your brain recognizes as sound. You ear consists of three major areas: outer ear, middle ear and inner ear. Sound waves pass through the outer ear and cause vibrations at the eardrum. The eardrum and three small bones (the smallest bones in your body) of the middle ear - the hammer, the anvil and the stirrup - amplify the vibrations as they travel to the inner ear. There, the vibrations pass through fluid in the cochlea, a snail-shaped structure in the inner ear. Attached to nerve cells in the cochlea are thousands of tiny hairs that help translate sound vibrations into electrical signals that are transmitted to your brain. The vibrations of different sounds affect these tiny hairs in different ways, causing the nerve cells to send different signals to your brain. As fluid moves, the cells activate a nerve that goes to the brain. That's how you distinguish one sound from another.

There are usually two types of hearing loss - conductive hearing loss and sensorineural hearing loss.

Conductive hearing loss is caused by damage to the ear caused by wax build-up, fluid in middle ear, ruptured ear drum or infection. This is usually temporary and can be resolved by medical treatment. It can also occur because of some mechanical problem in the external or middle ear. For example, the three tiny bones of the ear may fail to conduct sound to the cochlea or the eardrum may fail to vibrate in response to sound. Otoslerosis is a type of conductive hearing loss. It is usually a hereditary loss in which the tiny bones of the middle ear no longer transmit sound properly from the eardrum to the inner ear. Injuries such as car accidents may break these bones with a similar result. Surgery (done under a microscope) often produces remarkable results with this type of loss.

Sensorineural hearing loss is caused by damage to inner ear (cochlea). Causes may include aging, exposure to excessive noise, drugs, head trauma, infections or defects. This type of hearing loss is more devastating and is usually permanent. The tiny hair cells (called cilia) that transmit sound through the ear have been damaged. These hairs do not heal, so be careful when you are around loudnoises!

Most hearing loss results from damage to the cochlea. Tiny hairs in the cochlea may break or become bent and nerve cells may degenerate. When the nerve cells or the hairs are damaged or missing, electrical signals cannot transmit to the brain properly and hearing loss occurs. Higher pitched tones may become muffled to you. It may become difficult for you to pick out words against background noise.

Here's a good analogy that I found: "the damage done to the hair follicles in your ears are like blades of grass. When you walk on the grass, the individual blades are bent and matted down. The blades will rise by up again in time if they are left alone, but if you continue to walk on the grass the blades will break and die. The same is true for the hair follicles in your ears."

So be careful around loud sounds!

Val Bedard has a profound hearing loss since birth. She owns her own business Hear Well Services Ltd. (http://www.hearwell.ca), sells assistive listening devices for the hearing impaired, can be reached via email at info@hearwell.ca or by telephone at 1-888-549-2092.

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