How We Hear... Part 1

Have you ever stopped to think about how incredible your ears are?  The fact that we can hear at all and with such amazing clarity is really a miracle of design and function.  Let's talk a little about how our marvelous ears work.

To hear sound, your ear has to do three basic things:

•Direct the sound waves into the hearing part of the ear

•Sense the fluctuations in air pressure

•Translate these fluctuations into an electrical signal that your brain can understand

The pinna, the outer part of the ear, serves to "catch" the sound waves. Your outer ear is pointed forward and it has a number of curves. This structure helps you determine the direction of a sound. If a sound is coming from behind you or above you, it will bounce off the pinna in a different way than if it is coming from in front of you or below you. This sound reflection alters the pattern of the sound wave. Your brain recognizes distinctive patterns and determines whether the sound is in front of you, behind you, above you or below you.

Your brain determines the horizontal position of a sound by comparing the information coming from your two ears. If the sound is to your left, it will arrive at your left ear a little bit sooner than it arrives at your right ear. It will also be a little bit louder in your left ear than your right ear.

Once the sound waves travel into the ear canal, they vibrate the tympanic membrane, commonly called the eardrum. The eardrum is a thin, cone-shaped piece of skin, about 10 millimeters (0.4 inches) wide. It is positioned between the ear canal and the middle ear. The middle ear is connected to the throat via the eustachian tube. Since air from the atmosphere flows in from your outer ear as well as your mouth, the air pressure on both sides of the eardrum remains equal. This pressure balance lets your eardrum move freely back and forth


The eardrum is rigid, and very sensitive. Even the slightest air-pressure fluctuations will move it back and forth. It is attached to the tensor tympani muscle, which constantly pulls it inward. This keeps the entire membrane taut so it will vibrate no matter which part of it is hit by a sound wave.

The compressions and rarefactions in sound waves move your eardrum back and forth. For the most part, these changes in air pressure are extremely small. They don't apply much force on the eardrum, but the eardrum is so sensitive that this minimal force moves it a good distance.


The cochlea in the inner ear conducts sound through a fluid, instead of through air. This fluid has a much higher inertia than air -- that is, it is harder to move (think of pushing air versus pushing water). The small force felt at the eardrum is not strong enough to move this fluid. Before the sound passes on to the inner ear, the total pressure (force per unit of area) must be amplified.

This is the job of the ossicles, a group of tiny bones in the middle ear. The ossicles are actually the smallest bones in your body. They include:
•The malleus, commonly called the hammer
•The incus, commonly called the anvil

•The stapes, commonly called the stirrup

When air-pressure compression pushes in on the eardrum, the ossicles move so that the faceplate of the stapes pushes in on the cochlear fluid. When air-pressure rarefaction pulls out on the eardrum, the ossicles move so that the faceplate of the stapes pulls in on the fluid. Essentially, the stapes acts as a piston, creating waves in the inner-ear fluid to represent the air-pressure fluctuations of the sound wave.


This amplification system is extremely effective. The pressure applied to the cochlear fluid is about 22 times the pressure felt at the eardrum. This pressure amplification is enough to pass the sound information on to the inner ear, where it is translated into nerve impulses the brain can understand.

The cochlea is by far the most complex part of the ear. Its job is to take the physical vibrations caused by the sound wave and translate them into electrical information the brain can recognize as distinct sound.

Next time, we'll learn about how the cochlea translates that physical energy into electrical information...

This Year I Will...

During the last three days back at work, I think that I have written 2010 instead of 2011 nine out of ten times.  I can't believe that we are in a new year already!

January is the month of resolutions.  Things we all do for a week or two, and then find ourselve back in our old ways.  (I wonder just how many people are on diets right now that weren't on them a month ago?)  Why is it that we all make goals that we realistically won't keep?

One simple resolution that can make a huge difference for many people-- not only personally, but to their families as well is the goal to hear better.  Studies have shown that it takes an average of 7 years from the time a person first notices a hearing loss until the time where they actually do something about it.  During those 7 years, gradual changes take place where the person finds themselves less in touch with their family and friends, not as engaged in their work or social lives, and generally socially isolated.

Don't let 7 years worth of damage done by hearing loss affect your life.  We always tell our patients this-- we promise that your hearing loss is much more noticeable then the nearly invisible hearing technology that we have available now. 

"Resolve" to hear better today!!

New Study Indicates New Reason For Age-Related Hearing Loss

Millions of tiny sensory heir cells in the inner ear enable you to hear. Age-related hearing loss involves the death of some of these sensory hair, nerve and membrane cells. Since the hair and nerve cells do not regenerate in humans, their death leads to permanent hearing loss.

Researchers in the USA have now, with the help of research on mice, found out that these sensory hair cells can be destroyed if the so-called mitochondrial membrane, which protects the cells, is destroyed. This can occur if there is too much Bak protein present. Should this happen, proteins can find their way into the cells and break them down, causing the cells to die. Bak is typically induced by oxidative stress and its levels increase as people age.

So if oxidative stress triggers damage and death of hearing-related cells, enhancing the antioxidant defences of the mitochondria should reduce such damage, says postdoctoral researcher Jinze Xu, one of the researchers behind the study.

The studies with the mice show, that older mice without Bak protein have the same good hearing as young mice.

It is estimated that in the USA alone more than 28 million Americans will be affected by the condition by 2030.

Source: www.eurekalert.org, www.pnas.org