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This article assumes that you already know something about tinnitus, at least that it is ear ringing or some other unwanted ear noise that has no external stimulus or source of sound, and that you would like to know something about how our hearing works to get a better understanding of tinnitus, what causes it, and what can be done to stop ringing ears. The focus of this article is the inner ear and tinnitus. Two other articles deal with tinnitus and the outer ear and the middle ear, and they may be found under my author name. Having said that, let's get right to the inner ear. Fluid In Ear Tinnitus
So far, we have seen how sound waves are gathered by the outer ear or pinna, and they follow the funnel-shaped auditory canal until they come into contact with the eardrum or tympanic membrane. The tympanic membrane then vibrates with the energy of that sound, and transmits it to the middle ear via the ossicles,those three tiny bones, the hammer, anvil, and stirrup, which amplify and focus the sound, leveraging the sound energy for when the stirrup or stapes strikes the cochlea, which takes us to the starting point of the inner ear.
Until they reach the inner ear, the sound vibrations travel through air which is much easier than traveling through water, but when the sound reaches the inner ear, it encounters a fluid medium for the first time. That's why that amplification done by the middle ear is so necessary--so that the sound energy can overcome the greater inertia or resistance posed by the denser fluid medium of the inner ear. And, here in the inner ear, the way that the sound continues its journey to the brain changes significantly.
The inner ear is commonly called the labyrinth because of the shape of the cochlea. The word cochlea literally means "snail" or "spiral shell," and that's what it resembles. It is inside the cochlea where the mechanical vibrations are transduced or converted to electrical nerve impulses which the brain will then process as hearing.
When we get inside the cochlea, we find three fluid filled tubes. Two of them, the vestibular canal and the tympanic canal, transmit the pressure caused when the stapes presses against the oval window of the cochlea. The third canal, the cochlear duct, houses the sensitive organ of corti, which detects pressure impulses and responds by sending out electrical impulses which travel along the auditory nerve to the brain. These three canals, tubes, or ducts, are curved together into the snail shell shape, giving the cochlea its form. These canals are separated by a thin membrane, called the basilar membrane.
The basilar membrane functions as a base for the sensory cells of hearing, the hair cells of which there are about 20,000. These hair cells react with the various frequencies of the sound waves that are being transferred through the cochlea, creating tiny electrical impulses. Then, the organ of corti is housed within the cochlear duct, and it's located on the basilar membrane. It operates something like a microphone, sending electrical impulses along the auditory nerve to the brain, which interprets those impulses as the sounds that we hear. That's really about all we need to know about the sense of hearing for our purpose of understanding tinnitus better.
If you've been finding this look at hearing fascinating, and would like to dig deeper into the subject, I certainly understand. Wikipedia is a great place to start, if you want to go deeper. Not only does it offer good information, but it offers numerous additional references to take you as deep as you want to go. But, for right now, let's stay with our focus on tinnitus.
We now turn our attention to that other part of the inner ear, the vestibular system, that deals with balance and dizziness, because that can be associated with certain forms of tinnitus. Fluid In Ear Tinnitus
The way our inner ear enables us to hear is amazing enough all by itself, but this incredible little component of the body is also command central for the body's mechanism of balance. Certain other functions of the body also contribute to balance, such as the sense of sight, and input from muscles, but the vestibular system of the inner ear is the centerpiece for maintaining balance.
The vestibular system has three essential parts: the utricle, the saccule, and the 3 semi-circular canals or ducts. The utricle and saccule determine the position of the head at all times. That function is important for keeping the head in line with the body. The utricle and saccule are both sensitive to gravity and acceleration. Because of the way they are situated, the utricle detects changes in horizontal movement, while the saccule detects changes in vertical movement, such as when you ride in an elevator. Working together, these two, tiny organs keep track of head movement in all 3 dimensions, and keep the brain informed, and that helps us to keep our head aligned and our bodies in balance.
The way these organs actually work is yet one more marvel to keep us amazed. These little bodies, the utricle and saccule, are filled with tiny calcium carbonate particles suspended in a thick fluid. They are also lined with tiny hair-like receptors. When the head moves, gravity causes the weight of the particles in the fluid to press upon the hairs, which in turn send signals down nerve fibers to the brain, and the brain interprets the motion. The brain can then determine the orientation of the head by comparing the information coming from both ears, and it can tell if the head is simply being tilted or if the entire body is moving. Of course, the brain can use input from the eyes and muscles to help make its assessment, but the inner ear is doing by far most of the work for keeping the head aligned with the body, and keeping the entire body in balance.
At the same time, the three semi-circular canals or ducts are serving much the same purpose. But instead of focusing primarily on head position, they are providing information about the body's movement overall. These three semi-circular ducts are called, superior, posterior, and external. These canals or ducts are all perpendicular to each other, so that they are aligned with all three spatial dimensions, taking into account any motion that is forward or backward, left or right, or up or down, or any combination of motions. The semi-circular canals work pretty much the same way that the utricle and saccule work. The canals are also fluid filled, and have receptor hairs that respond to motion, gravity and acceleration, and send their messages along nerve fibers to the brain.
The tiny inner ear does all of that work, all of the time, whether we're thinking about it or not. We depend upon our sense of balance, and the vestibular system is gathering all of that information provided by the inner ear, and passes it on to the brain. In turn, the brain interprets the data and makes sense of it all, sorting out all of the competing signals, and sending out its own information to the muscles, to keep us in balance at all times.
When balance and tinnitus both become problematic together, it's often an indicator of Meniere's Disease, which accounts for nearly one percent of all tinnitus cases. However, much more common is another tinnitus issue that develops in the inner ear, namely noise-induced damage to the tiny hair receptor cells in the cochlea, and noise damage or acoustic trauma accounts for 80-85% of all tinnitus cases. Except for freak accidental exposures to excessively loud noise, noise damage is mostly preventable by avoidance of loud sounds or by using ear muffs or ear plugs to protect your ears. Fluid In Ear Tinnitus
Fluid In Ear Tinnitus - Tinnitus and the Inner Ear
