When an action potential is initiated these ion channels go from their closed state to their open state, when they open sodium can now pass through.

当动作电位形成时,离子通道,从关闭状态转到打开状态,当通道打开时,钠离子就可以通过

耶鲁公开课 - 生物医学工程探索课程节选

Now, sodium and potassium don't ordinarily move across membranes, they're charged molecules, they can't dissolve, they can't permeate through a cell membrane, but they go through because there are channels that allow them to pass through in the membrane.

钠和钾通常是不能跨过细胞膜的,它们都是带电粒子,它们不能溶解在细胞膜中,不能渗透通过细胞膜,但它们之所以能通过细胞膜,全赖膜上离子通道的作用

耶鲁公开课 - 生物医学工程探索课程节选