THE INNER EAR
As we continue our journey into the ear, let’s revisit what we have already discussed. Sounds created by compression and rarefaction in the atmosphere are collected by our ears - namely the pinnae or external protrusion of the outer ear. This sound travels down the funnel-like ear canal until it reaches the ear drum. This tympanic membrane vibrates in response to the moving air particles that make up sounds waves. This vibration puts into motion the Ossicles - the tiny bone structures that transfers the mechanical energy of sound and amplifies it as it passes through each in turn: the malleus, the incus, and the stapes. Once the stapes receives the amplified vibrations, it impacts the cochlea and brings us to the inner ear.
Up to this point, all sound has been traveling through air. But at the inner ear, sound will encounter fluid for the first time and the way in which it travels to the brain changes dramatically. The inner ear is commonly referred to as the labyrinth due to the shell-like cochlea that makes up the space. Much of the work of hearing is done in the inner ear, and it is the last stop for sounds as they make their way to the brain in the form of information.
The scala tympani, the scala vestibuli, and the scala media are the tubes in the inner ear, and they are curved together into a shape that appears like the shell of a snail. These tubes are separated by extremely thin membranes that move the sound along the tubes, and move the pressure that is created when the stapes moves against the cochlea as a whole. The basilar membrane is made up of tiny hair cells – there are tens of thousands of them, which react to differing frequencies in the sound that is being pushed through the cochlea. The hair cells identify resonant frequencies in the sound waves that are transferred through the cochlea. These create electrical impulses that are transported to the brain and interpreted as recognizable sounds.
Scientists are still working on a thorough understanding of just how the brain is able to interpret these electrical pulses into language, music, or just plain noise. The ear is a complicated and sophisticated system, which takes an external stimulus and uses mechanical energy to transfer that information to the brain. As we learn more and more about how we hear and what we hear, the ear appears even more remarkable!
MAINTAINING BALANCE
There is more going on in the ear than just hearing, though that one activity is amazing in itself. The ear is part of the body’s mechanism of balance that involves sight, input from the muscles, and the vestibular system of the inner ear. The vestibular system is the central command of balance in our bodies, and if things aren’t functioning correctly in this small part of the inner ear, it can mean big trouble for our whole body. It’s hard to imagine that an area so tiny could control so much! But, the inner ear is responsible not only for hearing, but also for maintaining balance.
The vestibular system
There are three semi-circular canals in the inner ear and these, along with the utricle and the saccule make up the vestibular system, which controls balance and gives us a sense of our body’s position.
If you have ever spun around to make yourself dizzy (or watched someone else do it), you were witnessing this system at work. The fluid in the semi-circular canals act in response to our movements: in this case the spinning. When you stopped spinning, the fluid kept spinning for a moment or two, or longer. If you were spinning for a long time, it gave you that “off-balance” feeling. You essentially played a trick on your vestibular system to make yourself dizzy, and your muscles responded to that trick by functioning incorrectly, and this is what made it difficult for you to stand or walk. Basically, your vestibular system was giving your brain the signal that you were still spinning, when in fact, you had stopped.
Let’s take a closer look at what happens in the inner ear with regards to balance to get a better understanding of the importance of this function.
The utricle and saccule determine the position of your head all the time, every moment of your day. As you turn your head from side to side, these two fluid filled cavities send signals to the rest of your body to adjust and adapt to the changes. We are designed to keep the head in line with the body, and these two do the work. They contain not only fluid, but also tiny hairs that are suspended in a jelly like substance as well as crystals or chalky substances that interacts with the hairs in the utricle and saccule. These crystals get pushed up against the hairs that are dependent on the movement perceived by the inner ear.
The three semi-circular canals serve much the same purpose, but they sense movement, rather than the head position. They are in perpendicular position to each other so that they are able to detect all types of movements, and send the necessary signals to the brain to maintain balance throughout the body. They also contain hair cells that act in response to the movement, and generate the information that is carried to the brain, and then to the muscles in your body to keep you from feeling dizzy.
The Other components
The inner ear is like home base for the system of balance we rely on every day, often without even thinking about it. The other components that work in conjunction with the inner ear are also essential to maintain balance and interpret the signals that originate in the inner ear.
Sight is an important factor in maintaining balance. Signals the inner ear is sending about head positioning and movement will generally be aligned with the signals your eyes are sending. It is primarily because of this that we see what we feel. In some situations however, there is a mismatch, and this can leave you feeling queasy and nauseous, or it can also give you a terrible headache. Consider the plight of the child with car-sickness. Sitting in a car may not look like movement in the way we normally think about it. In other words, the child isn’t running or spinning, or playing, but his body, particularly the inner ear, is sending signals that he is in movement. If he is looking down and reading while riding in the car, his eyes will signal that he is still, but his vestibular system is responding to every curve in the road. The sight doesn’t match the feeling and he will end up not feeling so good.
The cerebellum is the portion of the brain that is connected to the vestibular nerve, which transmits signals regarding balance to the brain. When a sudden loss of balance (such as missing a step on your way upstairs or stubbing your toe) occurs, the brain gets an instant message that there is danger to the system of balance. Involuntarily, you will move an arm or shift your weight to the other foot to keep your balance and avoid a fall. This is your vestibular system at work.
Your muscles are the final component in the system and when everything is working correctly, they receive the information from the brain to keep your body in line. Picture a child walking along a wall or a beam: the child will effortlessly know when to put a hand out to the side or how to correct his/her posture to keep balance and stay on the line. Now, picture an inebriated adult trying to pass a sobriety test. The person’s brain function is impaired by alcohol and the messages from the brain to the muscles are slow and fuzzy. No matter how much he/she tries, the person will be unable to walk a straight line by putting one foot in front of the other.