Got Science?

What causes nausea? The answer: other stuff.

There are a lot of things that can cause nausea. Nausea itself, though, is not a disease. Let me repeat this: (in general), feeling as though you're going to hurl is not a disease. It's a symptom, an indicator of something wrong, a sign from your body, but it's not alone (in other words, it's a hint for your doctor to figure out what's wrong with you.) Of course, it's not necessarily something really wrong with you, it could just be motion-sickness, but your body doesn't decide to throw up for no reason.

That leads me to the real point of the question: what causes nausea that is associated with motion-sickness? In other words, what causes motion sickness? Motion sickness is caused when the various places that collect information about your movement, position, etc. conflict with each other- primarily being, in order, your inner ear, visual input, and nerves around your body and in your muscles. When all these places send signals to your brain, your brain makes sense of it all to create a general idea of your movement. For instance, right now my brain can make sense of the fact that I'm sitting still, but my fingers are moving to type up this post. Therefore, my brain isn't confused and I don't feel sick. However, if for some reason my house suddenly got up and started walking, my eyes don't see that I'm moving because all I see is my house (frame of reference, anyone?). My inner ear, on the other hand, can feel that I'm moving as the house is, er, walking. They conflict when they get to the brain, my brain is confused, and presto! Motion sickness on the menu! I don't really know what happens in between the brain getting confused and nausea, but I'd guess that the reason why our brain signals our stomach to reject its contents is that it's so busy trying to figure out whether or not it's moving that it neglected the stomach. Just a guess...

Here are my links:
http://www.medicinenet.com/motion_sickness/article.htm
http://www.medicinenet.com/nausea_and_vomiting/article.htm