Why does the frequency of action potential decrease when threshold is reached slowly?

isyang94

please answer simple and descriptively

atyy

There are two "parts" to the sodium channel. Let's call these the "hole" and the "blocker". The blocker starts to move at a lower voltage than the voltage at which the hole starts to open. However, the blocker moves slowly, while the hole opens quickly.

When the voltage is increased quickly, the blocker begins to move before the hole starts to open. As the hole opens much more quickly than the blocker moves, it is opens fully and lets sodium ions into the cell, even though the blocker started to move before the hole started to open. Finally, the blocker moves into place, and even though the hole is still open, sodium ions no longer get into the cell.

In contrast, if the voltage is increased slowly, the blocker will finish moving in place before the hole opens. So you will be less able to evoke spikes when the voltage is increased slowly.