Human Hearing is Amazing
When we are born, we start off with about 20,000 hearing cells in the inner part of the ear called the cochlea. The cells are called “hair” cells. They are not hair as we have on our heads, or that some men have growing out of their ear canals. The specialized cells are called hair cells because under magnification they appear like short hairs growing in the snail-shaped cochlea. These hair-shaped structures that are part of the hearing nerves are called stereocilia.
When all these hearing cells are working properly, humans can hear sounds (in frequencies) as low as 20 cycles per second (or Hertz abbreviated as Hz) up to 20,000 Hz.
Younger people can usually hear the higher frequencies. You may have heard about the mosquito ringtones for cell phones. Those are ultra high frequencies that teenagers use so they can hear their telephone ring or alert them that they have a text message, but their (older) teachers cannot hear these high pitched sounds. Here’s why.
As we age, we begin to lose some of these cells. The hearing loss begins in those cells that are specialized for hearing the higher pitched sounds. These cells for high frequency sounds are the most easily damaged.
Here are some reasons these hair cells can become injured or die because of:
- Exposure to loud sounds
- High fever
- High blood pressure
- Cardiovascular disease
- Diabetes and Smoking
As these cells are injured or die, we lose our ability to hear some frequencies. Since this hearing loss is caused by the loss or injury to nerve cells this type of hearing loss is frequently referred to as a “nerve” hearing loss. The more accurate name for it is a sensorineural hearing loss.
As one ages, the hair cells for the highest frequencies are the first to be affected. At first the loss of the hair cells that specialize in the ultra high frequency sounds (above 8000 Hz) is not a great problem for communication. But as the damage creeps down into the areas of the lower frequencies (below 8000 Hz), speech sounds become increasingly involved. By the time the hair cells for the frequencies of 3000-4000 Hz, or lower, are affected.
An interesting note is a hearing loss is not even considered as a “mild” loss until 80% of our range of hearing (those effecting the frequencies higher than 4000 hz) has been affected.
The loss of these nerve cells usually occurs very slowly. Because it happens slowly, it is easy to not be aware of the change and to develop compensatory ways of dealing with the reduction of hearing. This is one reason those with hearing problems deny that there’s a problem: they are not aware of what they are missing.
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