The Vestibular System!

Welcome to the vestibular system tour! There are a few key stops along this ride, but to orient you properly, we’re going to start with the basics of the landscape.

Inner Ear 101

This here is the basic setup of the human ear’s innards. You have the outer ear, the middle ear, and the inner ear. Outer ear starts from the left, extends to the eardrum. Once you cross the tympanic membrane (eardrum,) you’ve reached the middle ear. Continuing in a rightwardly direction, you’ll hit a section called the round or oval window which may as well have a sign saying “you are now leaving the middle ear and  entering the inner ear. Population: 2. More or less.” Once you’ve hit that inner ear, you’ve reached your destination. So let’s go ahead and zoom in…

Inner Ear

Check out that grotesque mess! The inner ear is comprised of the bony vestibular system (the tangly octopus part on the left, also called the labyrinth) and the cochlea (the snail-shell looking right-half of this lovely illustration.) The cochlea is the organ responsible for hearing, while the vestibule/labyrinth is the stage for the elaborate play that inspired this blog. The vestibular system–the collective term for the semicircular canals and the vestibule–is the proud home of your balance, spatial orientation, and velocity sensor. This three-looped monster is nature’s  rather elegant answer to the GPS system. Basically those three loops (i.e. the anterior, lateral, and posterior canals) are filled with a fluid called endolymph that sloshes around when you change direction. Inside the base of the canals are these little hairs that float around like seaweed in the ocean… of endolymph. When a wave cooked up by moving your head comes by and bends the hairs, little nerves attached to the hairs take that as a sign to tell the brain “hey. We’re moving.” You may know this as rotational velocity. Three canals designated for up/down (anterior), left/right (lateral) and side-to-side (posterior) is exactly the number of canals you need to have three data points which will give you your coordinates in space, just like the XYZ-plane in 3-D Euclidean geometry. But the canals only give you info about rotation–you, dear reader, are more than likely capable of some sort of forward, back, side -to-side motion that we call translation (or linear acceleration for those of you savvy to the physics lingo.) Similarly to the canals, the otolith, or cavernous base of the vestibular system consisting of the saccule and the uticle, is coated in hairs floating around in the endolymph. But this endolymph is special! It’s heavy endolymph. Heavy with the burden of little calcuim crystals! These special calcium crystal-sensors get a special name: otoconia. It literally means ear dust. These puppies actually weight down the endolymph to a gel-like consistency that damps or absorbs most rotational ripples, but it’s perfect for picking up on the more subtle translational waves.   So, just like in the canals, the sloshing of that heavy fluid-gel through the otolith generates corresponding electrical impulses carrying messages of changes in speed and that shoot up the vestibular nerve to the central processing unit aka the brain where you almost instantaneously interpret this as your location. It’s all very pretty, no? Very clever! Until it breaks. That brings us to… 

What Happens When The Vestibular System Breaks? 

In a word? Chaos. Depending on how the system breaks and how badly, you lose all sense of where you are, where you’re going, and how fast you’re getting there. Running into things, collapsing, not being able to stand–these are all results of vestibular system malfunction. Visually, it looks and feels like the room is spinning out of control and opening your eyes leads to a dizzying array of blurred images. Motion sickness is fair game, which can mean nausea, headaches, and migraines. This experience is very specific to the person experiencing vestibular system failure, but the blanket term for the sensation of uncontrollable spinning is vertigo.

Vertigo can be caused by several other conditions entirely unrelated to the inner ear, so a through examination by a medical practitioner is required to establish the inner-ear connection to a case of vertigo. Because vertigo is a general symptom of a variety of causes, diagnosis of a specific inner ear malfunction can be a very long and often inconclusive process.

How Many Ways Can The System Break?

Too many. But there are some routes to failure that are more common and thus have names:

Benign paroxysmal positional vertigo (BPPV):  I like to refer to this as “ear rocks.”In BPPV, part of the heavy fluid (otoconia) in the saccule or uticule part of the vestibule becomes supersaturated with calcium crystals. When you supersaturate a solutin, it tends to form some big crystals from the leftovers it can’t absorb. If these get big enough, they can really move where they’re not supposed to. So say your calcium crystallized and traveled into the semicircular canals.  Meaning you now have solids floating around in the fluid that rubs up against the walls of the canals to signal motion to your brain. This is a mechanical problem, since solids are almost by definition not liquids and they tend to not flow so smoothly. This results in massive misinterpretations of small motions because the ear rocks are skewing the data. Congratulations, you have BPPV.

Meniere’s Disease (endolymphatic hydrops): The basic premise of Meniere’s is that a fluid called endolymph collects in abnormal amounts in the inner ear. They don’t really know why this happens, but it typically happens in the 40-60 age range if it does. Symptoms include tinnitus (ringing in the ear,) spontaneous hearing loss, spontaneous vertigo, auras, ear fullness, plus a whole batter of anxiety, vision, fatigue and  nausea issues. Meniere’s has no known cure. 

Perilymph fistula: Essentially, this is a tear in the membrane of the inner (or sometimes middle) ear. This can come from trauma to the head or too much pressure tearing the walls of the ear (you know when your ear won’t pop for too long, and when it finally does, it hurts like  motherf-er? Yeah that’s because the walls of your ear were under too much pressure, and sometimes it tears.)

*Labyrinthitis/ Vestibular neuritis*: AKA MY DIAGNOSIS. Vestibular labyrinthitis/neuritis evolves from an infection of some sort that inflames the inner ear and/or the connective nerves from the inner ear to the brain. It can come from a viral source ore, less commonly, a bacterial source. The distinction between labyrinthitis and neuritis is that the latter affects only the balance portion of the ear (the ironically, only the labyrinth) whereas the former takes everything–both labyrinth and cochlea. This means that in labyrinthitis, hearing is altered, or sometimes lost altogether. My diagnosis is vestibular neuritis–I can still hear quite well. It developed from a nasty upper respiratory infection I contracted in the summer of 2010. Neuritis generally goes away in 6-10 weeks, but in some cases (*cough* MINE *cough*) the virus/bacteria can damage the vestibular nerve and the condition becomes chronic (also classified as permanent.) Symptoms include violent onsets of vertigo, disorientation, nausea, vomiting, visual disturbances, etc. The Vestibular Disorders Association (VEDA) says this (correctly) about symptoms of chronic neuritis:

Many people with chronic neuritis or labyrinthitis have difficulty describing their symptoms, and often become frustrated because although they may look healthy, they don’t feel well. Without necessarily understanding the reason, they may observe that everyday activities are fatiguing or uncomfortable, such as walking around in a store, using a computer, being in a crowd, standing in the shower with their eyes closed, or turning their head to converse with another person at the dinner table.

Some people find it difficult to work because of a persistent feeling of disorientation or “haziness,” as well as difficulty with concentration and thinking.

There is no direct test for vestibular labyrinthitis/neuritis–it is therefore a diagnosis of elimination, which means it can take months for this diagnosis to be conferred onto a patient.

I won’t go into them on this site, but there are many other (albeit less common) vestibular disorders which include: superior canal dehiscenceacoustic neuromaototoxicityenlarged vestibular aqueduct, and mal de débarquement.

For more information on any of these topics, check out VEDA’s website, which is a fantastic resource for understanding inner ear disorders of every flavor and finding help for them.

Back to the Deets!

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