An action potential moves along an axon due to the sequential opening of voltage-gated Na+ channels. The diagram below shows voltage-gated Na+ channels separated by a short distance in the plasma membrane of an axon. Initially (left panel), only channel (a) is open. Within a very short time (right panel), channel (b) also opens. A diagram of two panels with an arrow between them showing Na plus ions outside a cell and inside a cell, separated by a plasma membrane with two Na plus channels labeled (a) and (b). In the first panel, the (a) channel is open and ions flow from outside to inside the cell. In the second panel, both channels are open. Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

What causes the second voltage-gated Na+ to open is the charge changes caused by the flow of ions through the first channel.

Explanation:

The second channel is a voltage-gated Na+ channel, we know that voltage-gated channels open their gates when there is a change in the voltage of the cell, by opening the first ion channel, there is a rush of ions to the inside of the cell that modifies the cell's voltage due to the new charges. The second channel is affected by this, and as a consequence, it opens its gates.

When depolarization occurs Na+ ion  voltage gated Channels opens.And under normal procedures, there is influx of sodium ions into the axonplasm. A brief refractive period must occur so that, there is a short period of tentative rest where the  Gated Sodium channels remains short.

However, if this period is not present as in this scenario,  as Na+  move in and out of  A, continuously, the ionic  distribution in  A, causes changes in  charge distribution in  B, which leads to opening of Na+ channels in B.

Explanation: