The vestibular labyrinth is the balance center located in the inner ear. About the size of a quarter, this delicate structure is made of three fluid-filled donut-shaped voids of bone called semi-circular canals, each jutting at a different angle from a central vestibule. (see figure)
The Vestibular Labyrinth
The loops make up a clever system for measuring how the head is turning. Tiny sensory cells called “hair cells” sit on small sails that project into the fluid from the wall of each loop. Just as the coffee in a mug stays still as when the mug is rotated quickly, the fluid in the semi-circular canals lags behind when the head turns, bending the sail and hair cells. When bent, the hair cells send a chemical signal to nearby vestibular nerve fibers, which in turn notify the brain that the head is turning. Because the three semicircular canals in each ear sense rotation best for a different direction, the brain can combine signals from all canals to accurately measure head rotations in any direction.
This information from the inner ear is very useful for keeping your eyes steady when your head is moving. When you are walking, running or driving, your vestibular system is constantly measuring head rotations and controlling eye muscles to as to turn your eyes left and up when your head turns right and down, etc. If this didn’t work, your view of the road ahead would bounce and jitter so badly that you couldn’t see well enough to drive. It is such a useful system that nature has maintained the structure of the vestibular system with very changes over millions of years of evolution. You have a vestibular system very similar to that of a cat, lizard, fish, frog or dinosaur.
Unfortunately, the vestibular system is so reliable that your brain is thrown off when the system isn’t working. In cases of Meniere’s syndrome, benign positional vertigo, vestibular migraine, infections, tumors, or other vestibular disorders, the distorted input from a diseased vestibular system can give you and your brain an altered sense of motion. You might sense an illusion of movement ( vertigo), or you might notice “shifty” or blurred vision as your eyes attempt to follow head movements that aren’t real. At best, this can be disconcerting; at worst, it can be severely disabling.