Many of us have been caught by surprise by a lightning quick swipe of a cat's claws, or cursed (quietly, of course) when a fly easily evades the swatter. How can anything move so fast? Well, one secret is size. Unlike the electrical current in a copper wire, nerve impulses, electrical though they be, are almost glacially slow in comparison. This is because molecular movements account for the nerve impulse, not the rapid flow of electrons along a conductor. Thus there is a small lag in time between when you send a command to curl up your toes (for instance) and the time the toes curl. If you're an NBA superstar at 7 foot plus, it's even longer (and pity the poor giraffe).
The nerves to the paw of the kitty busily shredding your pants leg has
only inches to go, not feet, and that makes all the difference in the world. This also
explains why a Roadrunner can take on a snake with relative safety, and how a kangaroo
rat can leave a striking rattler biting air.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.