Fink has long thought that we should be able to demand a lot more from the fibers in our clothes. So for a decade, his lab has been developing fibers that can interact with their environment. His newest creation, with Shunji Egusa, Noémie Chocat, and Zheng Wang, will be published in next month’s Nature Materials…The secret of the new acoustic fibers is that they’re piezoelectric.

Their piezoelectric properties come from engineering at the atomic level: Each strand of fiber has fluorine atoms only on one side, and hydrogen atoms on the other. The different in charge held by those atoms creates a “lopsided” electric field across the fiber itself.

Thus, when an electric field is applied to the fibers, they flex and change shape. And also vice versa: When the fibers change shape–due to a sound wave, for example–they emit an electric signal. “

Then, for whatever reason a stimulus triggers an action potential (it could be a neurotransmitter in the brain, light triggering the rods and cones in the eye, etc). That would be like the announcer guy saying over the PA, "Hey guys, start the wave in Section A."

Once that occurs, the nerve becomes DEpolarized in one section only (everybody in section A stands up). This is because of the Na ions that go rushing out and make that part of the neuron positive instead of negative (a person goes from seated to standing position).

This depolarization in one part of the nerve triggers the next part of the nerve to become depolarized next.(hey, why is everybody in the next section standing up and yelling "whoo?"). So Na ions rush out of the next part of the nerve cell based on charges and all that. But the original section now has to go back to normal. It's not the wave if you don't sit back down. So the first part of the nerve becomes REpolarized (K ions come rushing in and make it negative again). While section B is standing up, section A is sitting back down. And so on, each section triggers the next, and you get a wave like action. Just like random people sitting then standing is not the wave, random parts of the nerve changing polarity is not a nerve impulse. It takes a sequential, orderly progression of polarization-depolarization-repolarization (sitting-standing-sitting) to make an action potential (wave). You wouldn't see the crowd doing the wave unless people's movement was organized, just like how a cell transmits an impulse.

The one thing I haven't included is the refractory period. You'll notice that the nerve starts out negative due to a build up of Na ions on the inside, then locally becomes positive when Na rushes out. It becomes repolarized not because Na rushes in, but instead K (which is also a positive ion). The refractory period is the time in which the two swap places again, after the action potential has passed through (after people sit down after the wave they pick up their coats and programs and settle back in). This is why an action potential will not move backwards along a nerve.