sodium now can enter through new channels.

钠离子就可以经通道进入胞内
If there are a lot of these voltage-gated channels on the surface.

如果胞膜表面有大量这样的电压门控通道
They sense a change in voltage,

它们感受到电压变化
and they all open,

全部打开
one can have a dramatic change in the currents that flow

膜间的电流急剧变化
through the membrane and hence a dramatic change in membrane potential.

导致膜电位急剧变化
Now,that's exactly what happens when we have an action potential.

这就是动作电位的产生
I show you this diagram that I showed you a few weeks ago

几周前我就给你们看过这幅图表
when we were talking about the nervous system and how it communicates.

当时我们讨论了神经系统以及之间的交流
I explained it in sort of a superficial way then,

当时我只是简单的解释了一下
but now you can understand it a little better

现在你们就会有更深刻的理解了
if you think about it in terms of these--

如果你把这些和今天讲的细胞膜