Last month when I wrote the Barotrauma blog (which has become one of my most popular this year, thank you), I mentioned that I would write about perilymph. In the inner ear there is both a bony labyrinth and a membranous labyrinth (the green line on the diagram). The labyrinth consists of the semicircular canals (the balance center) and the cochlea (the hearing center). These lie beyond the middle ear where your little bones are- the malleus, incus and stapes (hammer, anvil and stirrup). The inner ear is where some of the most interesting things happen, and they happen in fluid. The perilymph fluid fills the space inside the bony labyrinth that surrounds the membranous labyrinth. The perilymph is high in sodium and lower in potassium. If you recall from high school chemistry or biology (I can’t remember that far back!), there is a sodium/potassium pump that keeps the levels where they should be. Remember this, as it becomes important later.
The second fluid in the inner ear is called the endolymph. The perilymph and endolymph fluids are separated by a membrane called the membranous labyrinth. As I stated earlier, the perilymph fluid is high in sodium and low in potassium with basically a negative charge. This is very similar to the cerbrospinal fluid surrounding the brain and spinal column. The endolymph fluid is the opposite, high in potassium and low in sodium which gives it a positive charge. When the fluid levels of the perilymph and endolymph are at an equillibrium, you have regular hearing and balance functioning so you hear well and are not dizzy!
What happens when they malfunction? Bad things such as Meniere’s Disease, or endolymphatic hydrops, is the most common. The links describe Meniere’s and some treatments available at this time. But ask anyone with Meniere’s and they will tell you that it is not a condition that can be easily dealt with.
This is not to say we cannot have a virus that affects the inner ear. This is called labyrinthitis or inflammation of the inner ear and will be my next topic!