The Vestibular System

This week on PopSiren I went a completely different direction from the first episode. Yea, sorry. No fire this time around, but we did play with a way for you to make your friends dizzy. Yes, I talked about the inner ear. And, I spun Neha around and around and around and…

The vestibular system is not just your inner ear, but consists of all the proprioceptive organs in the body. Proprioception helps your brain figure out where your body is in space. Normally, all the different organs work together very nicely, but sometimes one or more are disabled. This leads to trouble in spatial perception and balance.

In the show, I demonstrated how simply closing the eyes can remove one of the important markers of body position in space. Think I’m kidding? Just try spinning around with your eyes closed and see where you end up.

There is fluid in the canals of the inner ears called endolymph. When the head is still, so is the endolymph. When the head moves, inertia causes the endolymph to move in the opposite direction. So, if you are turning to the left, your endolymph is moving to the right, and vice versa, up, down, and round and round. In the segment on PopSiren I asked Neha to close her eyes. Then I spun her right round to her left. You can totally see that her eyes are moving to the right when I stop her and have her open her eyes.

The second demonstration didn’t work as well as I would have liked, but it did work. By having Neha put her head down while she’s spun around, I was isolating the posterior canals in her inner ear. If you look really carefully at her eyes when she comes to a stop, you can see them moving diagonally up and to the right for a moment. All triggered by the semi-circular canals. What do you think would have happened to her eyes had I asked her to put her head on her shoulder?

If I had the time, I would have also shown that Neha’s perception of direction would have been the opposite of her actual direction of movement. You can do this yourselves (those of you who are adventurous enough to give this trick a shot). Make sure you keep absolutely quiet during the spin, and  try to not jar the chair as you spin it. Then have the victim… ahem, volunteer indicate which direction they think they are moving with their thumb (to the right for right, to the left, for left, and straight up for no movement). Because the volunteer’s eyes are closed their sense of movement will come only from their inner ear, which as a result of physics is backwards. You can also play around with stopping the volunteer suddenly versus letting them spin slowly to a stop. See for yourself and let me know what you find.

I mentioned the otolith organs, the saccule and utricle, but never really explained them. While the semi-circular canals detect rotational movement, the otolith organs detect movement in linear planes (i.e. front to back, side to side, up and down). The endolymph of the otolith organs is interesting because it contains little particles called otoconia, which enhance the signal to the brain by making the endolymph in that part of the ear denser. Thus, causing greater shearing force to take place between the layer of endolymph and the layer with all the hair cells adjacent to it.

Now for how all this applies to you. If you are prone to motion sickness, you probably know all sorts of tricks to combat the sick feeling like sitting in the front of the car, being able to see the horizon, or pushing on a pressure point on your wrist. The reason that the tricks work is that you are using the other organs in your vestibular system (namely, the eyes and skin) to help override a mismatch between your inner ears and your actual state of motion.

I hope that everyone learned something new this week. I had a lot of fun with the show (nevermind that I actually got to co-host!!!) and the segment. Next week, I think I’m playing with magnets and explaining the basics about how they work.

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