When do grid cells fire?

[erickulcyk]

Hello,

I was reading the wikipedia page on grid cells, and I was a little confused on their function. First, how are grid cells structured (many or few dendrite, long or short dendrite/axon, etc..)? Also, it wasn't clear if,say, someone with no motor input would trigger these cells. For instance, if you were in a motorized wheel chair with a blindfold on. If the grid cells still fired then, that would indicate the expected motion of the chair along with the noise the chair probably triggered you realize you were moving. Now, put that wheelchair against a wall so it makes noise and the wheels turn but you go nowhere. If the grid cells don't fire, that would mean they are using built in accelerometer in the body.
Finally, if you are moving around in a video game, do these cells fire?

Thanks,
Eric