Hi! I’m your ear

December 8, 2014

Hi! I’m your ear.

OK, I know you have two. I’m your right ear, but I am talking to you with the full awareness, permission, and authority of my sibling, your left ear.

Why am I talking to you now? Well, I have some things to say for myself, on behalf of my sibling, your left ear, and the rest of your hearing (auditory) system while I still can. You see, when you hear from one or all of us otherwise, such as when we buzz, roar, or ring, it means that’s something is wrong. So, I’d like to take this opportunity now while things are still right and otherwise quiet.

When you think of me, you think of what you see hanging off the left and right side of your head. I know that because my cousin, your brain, told me so. Those aren’t really your ears; they’re only a part of the neighbourhood.

So, being self-centered, let me start by describing myself and I’ll get around to talking about my neighbours, some of whom are cousins, later.

When you were born, you had two sense organs that were fully developed: your nose and your ear.

Your eyes were still a work in progress. In fact, so was your brain. (In fact, unless you’re over 25 years old, your brain is still a work in progress. Just ask the car rental companies.)

So, soon after you were born I started training my cousin your brain, by means of the 8th cranial nerve (don’t you just love it when I talk medical), to listen. The 8th nerve is also called the Auditory Nerve. That training is quite a job. Other than the signals I sent that are translations of the sounds I received, I had to send noises so that your brain could start making “sound maps” that would be useful later as you became aware of the world around you. You know things like recognizing your mother’s voice and in learning to understand what your mother was saying to you.

I knew this already, but there have been recent scientific studies as to the earliest age for a baby to recognize his mother’s face from the faces of others and the earliest age when a baby can recognize his mother’s voice. While a baby as young as three months can recognize his mother’s face, that baby already could recognize his mother’s voice after a few days and at 100% accuracy. Wow, I bet that comes in handy.

While on the topic of mothers, let me tell you two other things. While I can hear sounds while in the womb, even my mother playing music, my upstairs cousin, the brain, can’t make sense of them since those sound maps I have to send haven’t been formed. So enjoy the music, but don’t think that you are doing me any favours. The sounds I hear from my mother’s body are sufficient, thank you.

Second, is that I am the second oldest perceptual organ from an evolutionary point of view. Your sense of smell is developmentally older. Early life first needed to respond to chemicals around them to know whether they were about to eat or be eaten. Response to pressure changes in the surrounding fluids came second. Thus, those early animals that could respond to the chemicals around them and the pressure changes so that they were predator instead of prey lived to pass on their genes. Responses to chemicals became smell, and taste, and responses to pressure changes became hearing.  So much for history.

That scoop fastened to the outside of the head isn’t me. That just focuses sound for me. You can’t see me, or my sibling. I am located deep inside in the temporal bone portion of your skull; the hardest bone in the body. I am made up of a long curled-up tube that has a membrane-like organ dividing it and I am filled with fluid. I share the fluid with the balance system. Inside this membrane-like organ, called the organ of Corti (because Corti was the first person to describe it) are 30,000 hair cells, I have only 5,000, called inner hair cells, that send information to the brain to be processed as sound; speech, music, Harley-Davidsons, etc. The other 25,000 are there to tune the system for optimal hearing precision, both in terms of loudness and pitch. They are called outer hair cells. Think of them as fast-responding pre-processors so that my 5,000 inner hair cells can send the best and most accurate information on up to the brain. To keep my 30,000 hair cells active and healthy are about 500,000 other cells and structures.

I am up and working 24/7/365 for as long as you live. I don’t get time off. You have no earlids you can close to shut out sound. Even if you did, I’d be hearing the sounds the rest of your body makes anyway. It’s pretty noisy in here all of the time what with your breathing and pulse. My cousin the brain has a habit of turning off processing what I am sending so that you can sleep, but I am sending anyway.

The way I send information to the brain is via the lower portion of the Auditory Nerve. The balance system gets the upper portion to send its information.  Here is a sketch of me, my neighbours, and my cousins. I am the part coloured in violet and labelled cochlea.

Ear Drum

The way I get sounds is pretty fantastic from an engineering point of view.

Remember, I said that I was filled with fluid. You don’t live underwater, so sounds come to you through air. If you have ever been in a swimming pool, a lake, or even the ocean, when you completely submerge your head underwater, you can’t hear the sounds above you up in the air very well. That is because when sound strikes a surface such as water, more than 99.99% of it is reflected away and only 0.01% of it gets into the water.  Same with me. If sound came directly to me without first getting managed by my neighbours, you would have a hearing loss of at least 40 dB (that means enough so that a person whom you can now hear clearly when talking to you from a yard (about 1 meter) away would now have to be 4 inches (10 mm) away to sound as loud).

So, who are my neighbours participating in this engineering marvel?

Coming from outside of your head, what you call your ear is often called the pinna or auricle. Scientists, as recently as in the 1970s, thought the pinna to be a vestigial organ (in other words not very useful), sort of like they did the appendix in your gut. Now they know, and I have known all along of course, that the pinna is vital for collecting sounds, particularly those in the higher frequencies, and doing so in such a way that the brain can make use of the information I send. With the pinna, you can tell if sounds are coming from in front or from in back. Without the pinna, you can’t. And while some animals can move their pinna to allow hearing to be more directional, we primates don’t have that ability or, apparently, necessity. It’s the bowl of the pinna that is especially useful for getting high-frequency sounds to me.

Connected to the pinna is the ear canal. It is a tube a little over an inch long (2.54 cm). It has two primary, albeit passive, functions. First, it provides a stable temperature at the eardrum. This is important, because if the temperature at the eardrum were to change much above or below body temperature, my cousin the balance system could be affected and you’d get dizzy. Second, it amplifies sound in the higher frequencies where there is a lot of low-intensity information in speech. The ear canal is lined with skin, the same as the rest of your body. The outer two-thirds of it has glands that produce oils that combine with dust, dirt, and sloughed off skin cells to make ear wax. There are hairs in the ear canal that work to push the ear wax out.

On behalf of the ear canal I’d like to inform you that only one thing smaller than your elbow belongs in your ear canal, an earplug to protect me from loud sounds. Keep your Q-tips® out! What happens when you use a cotton swab, hairpin, or unfolded paper clip to clean out your ear is that you can cause scratches that can become infected. And rather than clean it out you can push the wax in further and, once inside far enough, it’s not coming out on its own. It can stay to form a dam, trap water behind it, or just pack up enough to completely close off the ear canal, giving you a hearing loss. Plus, even if you do succeed in getting the wax out, you’ll eventually rub off the hairs that are supposed to push the wax out on their own. So, keep out everything other than earplugs and if wax comes out when you remove an earplug, clean off the earplug.

At the end of the ear canal is my eardrum.

Its outer surface is a thin lining of skin, its middle structure is made of fibres to give it shape, while its inner surface is made from mucous tissue like the lining of your mouth. That starts the middle ear, which is an air-filled space that contains, among other things, three small bones, the ossicles, the smallest bones in your body. They are set up in a lever arrangement with the end of the smallest bone connecting to me. As sound strikes the eardrum, it is converted to vibration that is delivered to me. The ratio of the area of the ear drum to that of the plate of the small bone driving me is 30:1. By the time I get the vibes, most of the 99.99% of sound that would have been lost has been recovered, well at least 98% of it.

So, I get the good vibes courtesy the eardrum and the ossicles and convert them into neural information and send that information up the 8th nerve to the brain. Remember, I’ve trained the brain to listen; that is, make sense of what I’m sending. Along with what my sibling on the left side sends, I can let the brain figure out from which direction a sound is coming: left, right, up, down, front, back, or on the side at 30 degrees to the right, from slightly above me, and moving. The brain can sort out speech from noise if I send the correct information.

Remember the bit about earplugs?

You need to know this: I am the most active organ you have. That is, I consume more oxygen and nutrients, allowing for my weight, than any other organ your body has, including my cousin your brain. If you’ve ever been deprived of oxygen, you may have notice the first thing to happen is that sounds become distorted and you may even have heard a buzz.

The range of sound pitches I can process range from just above vibration at 15 cycles per second (now called Hertz – abbreviated Hz – after a German physicist) to more than 20,000 Hz. At least I could when you were born. I can also hear sounds so soft as to be near the random noise air molecules make (called Brownian motion after another physicist) to as loud as the noise from a rocket being launched.  When sounds become too loud for me to handle safely, I can have the brain send a message back to two muscles in the middle ear to change the lever action of the three bones of the middle ear, reducing their efficiency. But this takes time, so I get the initial insult from loud sounds.

Notice that I used the word insult. That’s just what loud sounds are. Once the sound gets above a certain level, it’s simply too much for me to handle cleanly and safely. It’s the equivalent of a light being too bright, and this trick with the middle ear bones is similar to squinting and really no more effective.

If these sounds are loud enough and long enough, I get bruised and you lose some hearing for a while. I may be sending other sounds related to the bruising to the brain and you’ll perceive these as a ringing, buzz, or a roar. Your hearing will sound muffled. Give me a rest and I’ll recover, but not without a mark. Some of my 2500 inner hair cells may not come back. They’ll die. They won’t be replaced. All of the hair cells I had the day you were born is all that I am ever going to get.

Now, for a while, I can work around the loss of hair cells.

Between me and the brain, we can cover for the loss so that you won’t notice it. But, eventually, when enough are lost, when I am bruised and battered by loud sounds, we won’t be able to work around the loss and you’ll begin to develop a loss of hearing. I’m designed to work best when the loudest sound I hear is you, your voice. I need protection from regular exposure to sounds louder than your voice or I’ll get bruised, giving you a temporary loss of hearing. Eventually, I’ll be battered and that hearing loss will become permanent.

There is a cultural myth that implies that everyone loses their hearing as they age to the point of being deaf. It’s a myth because it’s not true. Yes, when I’m 85 I won’t be as spry as when I was 8 or 18, but I’ll still be functioning well enough for you to hear your grandchildren and the song birds in the neighbourhood.  You shouldn’t have to crank up the sound of the television to the point where your neighbours hear the evening news from your TV.

But, to get to that point, there are few conditions. First, you need to be healthy and free from disease. I don’t mean that you need to go to extremes, just stay well. Second, if you’re from a family that is predisposed to loss of hearing – we don’t understand it, but some people are – then pay close attention to your hearing. Third, protect me from loud sounds. As a rule of thumb, if you have to raise your voice to have a face-to-face conversation with someone more than 1 yard (meter) from you, you need to be protecting me. You can do that two ways: 1) get away from the noise or 2) use your earplugs or earmuffs (or your fingers to plug up your ears if necessary) to reduce the noise I get.

While really loud music may be entertaining, it hurts me.

You generally can’t play music loud enough on your home stereo to be hurtful to me. Someone will be telling you turn it down or it won’t sound goodEar at high level anyway. But you can play your earphones on your music player (iPad, iPod, Chip, Geek Wave, or even your smart phone) loud enough. You can also install a car audio system that plays loud enough to impress your friends, annoy your neighbours, and hurt me. Instead of turning it up to 11, turn it down to 5.

You can also be exposed to dangerously loud music at live concerts.

If you’ve noticed that the performers are wearing custom earplugs for their monitors, you should be wearing your earplugs to protect me. The same goes for sporting events where fans are constantly engaged in cheering or jeering such as hockey or football. Further, there is no such thing as a tractor pull or automobile race that is quiet enough to be safe for me, so take your earplugs with you as you leave for the event.

Do you like to hunt or shoot?

The loud crack from the weapon firing may be satisfying to you, but it hurts me. You like working with hand tools? Do you realize that the sound of each hammer blow hurts me? So the great feeling you get from driving a nail or breaking down a wall for home rehab doesn’t feel so good to me. Power tools, lawn mowers, leaf blowers and such are also dangerously noisy for me. So, as a rule of thumb, if you’re going to protect my cousins, your eyes, protect me.  If you have to shout to be heard over the noise, PROTECT ME.

If you do notice that I am losing it, act early.

Please, don’t be vain, don’t be a denier. See a hearing-health professional and ask about getting me some help (a hearing aid). The less time that the brain and I have to work around your loss of hearing, the better you’ll do with a hearing aid. While you’re at it, become extra aggressive about protecting the hearing you have left. I came into this world when you were born ready to go and just needed to complete some training for your brain on how to listen.  I plan on sticking around as long as you do, so a little help would be appreciated.

Stay healthy, avoid loud noises and music, and use hearing protection when necessary, and my sibling over there on the left and I will be here working 24/7/365 as planned.

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