The larger file is very slow on most computers, its primary use is recording to VHS tape.

The round bottom is due to the amount of stimulus that neurons need before they reach their threshold. As the impulse procedes downward the more intesely firing red neurons in the center cause the neurons below them to reach their threshold faster, the less intense bluer neurons around the sides don't do this as quickly and form the rounding shape you see. The ripple effect in the center is due to neurons reaching their maximum firing rate and thus not able to receive very much stimulus the next frame. We have a row of high red neurons firing on a row of low blue, the next frame the not ready reds are more blue and the ready blues are more red. The tapering off on the top of the impulse happens as the neurons bring their sodium and potassium gradients back to normal.