OK, I know why people get motion sickness - the body’s balance system gets screwed up, visual cues don;t match those from the inner ear, etc etc, but my question is… why does this lead to vomiting?
Is there any physiological reason why the body thinks it’s a good idea to jettison a perfectly good breakfast just because it can’t work out which way it’s moving? Why not some other symptom? I can understand the body wanting to remove stomach contents if they are causing some damage due to being poisonous or contaminated, but what has motion got to do with anything?
Or is throwing up just an all-purpose “Something’s not right here” response hardwired into the brain? I’m lucky in that I don’t seem to suffer from motion sickness, but I know people that could get sick on a boating lake. It’s not just humans either… my parents’ cat gets sick if it has to be carried in the car for more than 10 minutes.
I’m not sure if I’ve really explained myself clearly here, but what the heck.
I don’t remember where I got this, but IIRC, the U.S. Air Force did some testing on this phenomena, and I think they came to the conclusion that the part of the brain that handles vomiting, and the part of the brain that handles balance/motion are side by side. In some people the barrier between the two is too thin and the signals from the rapidly firing balance section during moments of “duress” cross over and stimulate the vomit control portion.
Interesting. I guess the USAF has something of a vested interest in this kind of thing - they don’t want millions of bucks worth of airplane taken out of commission by some goofball spewing on the instrument panel…
As I recall from quizzing a neuro prof, the basic answer was that no one is really sure. The hypothesis he put forth, which quite frankly makes a little more sense to me than the one promoted by the fine folks over at the USAF, is that motion sickness mimics the effects of intoxication. Prior to the “modern era” (e.g., for the vast majority of our evolutionary period), the only time one was liable to experience similar symptoms was when one had just eaten summat that wasn’t exactly a good thing to eat. Hence jettisoning that last meal was an extremely good idea. Motion sickness would therefore just be an unfortunate triggering of what’s really still a very useful reflex.
It seems to me I read somewhere that the semi-circular canals are unusually sensitive to toxins and the body relies on them to tell when to hit the big white telephone. Then if they get upset for any other reason, they react the same way. I guess sailors eventually learn not to react, but humans have been sailing for only about 50,000 years (and regularly for less than 10,000) so evolution has not caught up.
As with the opinion on why motion sickness occurs in the first place, it is also not entirely clear why antiemetics work. As with most drug fields, there’s a relatively broad spectrum out there, and there appear to be reasonably good guesses on most of them, but the mechanism of marijauna, in particular, seems to be completely unknown. Those that we do have an understanding of all appear to block or inhibit some step in the chemoreceptor pathway that triggers the emetic reflex - basically there’s a receptor that monitors toxin concentrations in bodily fluids, and it’s that sucker that cues you to call uncle Ralph.
To provide a concrete example, scopolamine, commonly used for motion sickness, is an anti-cholinergic drug - but it ain’t really clear how that helps anything. In other words, we know what it does at one end (the immediate drug effect) and what it does at the other (no yakking), but not the connection. Check out the link for a bit more info. It’s probably worth noting that “science” is a bit unclear on exactly how the whole vomiting mechanism functions, too - so you can see just how lucid this entire thing is.
Just to address a side point, the semi-circular canals that Hari Seldon refers to in the inner ear sense angular acceleration, and thus the potential “reeling” due to motion or intoxication, but not the actual toxins themselves.
Another spectrum of antiemetics appears to work by blocking the anticipatory effects of certain situations, such as chemo patients who feel nauseous as they approach the hospital. In other words, they’re probably not acting on quite the same chemoreceptor pathway, but rather on some branch of it that is modified by “higher” brain functions.
Also, the standard IANAPharmacologist should be offered. I’ve just had to sit through way too many class hours recently. But now it’s over. OVER. Muh-wa-ha-ha-ha. Who? What? Me enjoying Xmas break? Never…
I’ve always favored the theory that the vomiting response developed because, prior to recent eras, about the only thing that would cause the wobblies was ingested toxins. In which case vomiting could well be a very useful survival trick. (This would also tie in with pregnant women and morning sickness, the idea that the developing fetus needs to be protected from toxins so the mother’s sensitivity to such things is ratched up for a time)
But that doesn’t allow for the fact that one can become accustomed to motion, enough so as to completely kill the nausea of motion sickness. In fact, the air force cures motion sickness by forcing those prone to it to fly many hours a day, though all sorts of gyrations, until the recruit either stops puking or gives up (or a flight surgeon stops the process to protect the recruit’s health)
I have been trying to find a cite for my first response, but curse my dial-up access, I can’t find any.
It may have been a Reader’s Digest article I read a while back, but here is an interesting article regarding learning how to cope with motion sickness.
