Tuesday, April 6, 2010

Stamps of Our Lowly Origins: Exhibit 1

Intended as one in a long series. I'm studying neurology in med school this quarter. The nervous system is interesting, not least because it does a lot of things without our being aware or in control of them. I'm not just talking about not being aware of your own breathing (which you suddenly are, and will be for another sentence or so), but reflexes that use what are otherwise entirely voluntary muscles. For example: you're walking along and you step on a nail. You raise the injured foot, straighten the other leg, and rebalance yourself in less than a second; the reflex arc transits through the spine without passing through the brain, just like the classic knee-jerk. No one had to teach you that, and you don't even have to think about it.



In people with spinal cord problems, these reflexes become more pronounced, because they're less modulated by higher brain centers. Consequently, if you have a spinal cord injury and something sharp unexpectedly pricks you on the top of the foot, you respond the same way - by lifting that foot up, straight into the sharp object! Strange, right?


Quiz time - multiple choice. This reflex to move the foot toward the painful stimulus makes sense if:

A) We were created in our present form by a super-being with either really bad engineering skills or a cruel sense of humor.

OR

B) Our ancestors were toe-walkers and what is now the top of our feet was actually the side of their hind paw, so it made sense to lift the foot up if a painful stimulus was incident on that surface (from the side), and because evolution is not perfect, some of our reflexes remain the same even though our limbs are now oriented differently.

More important than understanding the origins of this reflex is the impact on the choices we make about our health. Some folks won't want to accept B, but those folks should really consider whether modern medicine is right for them, because this is what they're teaching everybody in healthcare professions around the world.

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