Last week I asked: what could go wrong with the vestibular system. I was hoping to have a more satisfying answer by now, but I haven’t. So here are some random wanderings.
The scientifically suspect book my scientifically suspect first sensory integration therapist gave me suggests “underinflation of the endolymphatic sac”, without anything so droll as a definition of the endolymphatic sac. No problem, I have the internet. Wikipedia’s entry on the subject is… weak. I originally misread it as saying the endolymphatic sac was connected to only the saccule (one of the two linear-motion detecting mini-organs). The Pictorial Guide To Cochlear Fluids sets me straight on this: all of the various vestibular systems are interconnected, and they all connect to the endolymphatic sac.
An underinflated endolymphatic sac would imply an insufficient amount of endolymph- either because you’re not producing enough, you’re somehow leaking it, or you need extra for some reason (extraordinarly large semicircular canals? I don’t know). The various vestibular structures can’t have their fluid levels too tightly coupled, because that would ruin their specificity, but they are connected via endolymph ducts. It would (famous last words) make sense if they all had some ideal fluid level, and overflow went into the endolymphatic sac.*
Dr. Internet has pointed me to many descriptions of how an excess of endolymph is bad for you. And it’s not hard to imagine how a deficit could hurt you. But is it possible to have enough for the vestibular system, and yet the endolymphatic sac is undesirably empty? Unscientific Book suggests that because the sac is directly touch with brain fluid, information is reported to the brain through it, and that an underinflated sac can’t do this. I can’t prove that’s not true, but it strikes me as unlikely to be a large effect. If I had more faith in the book I’d poke around more, but for now I’m going to leave it.
*Last week I implied the ortoliths (linear motion detecting systems) contained only gel, not endolymph. In my defense, I thought it was true. I was wrong.