What is a threshold potentional?

Question

What does it have to do with action potentional, too?

Answer 1

The threshold potential is the potential across a membrane that much be reached for the cell to fire an action potential. Imagine starting up a lawn mower. You can keep pulling on the cord (similar to generating a local potential), but in order for the mower to start (similar to the cell firing an action potential), you have to pull the cord a certain force for it to start. That force is the equivalent to a threshold potential.

What happens in a cell when the threshold potential is reached is that the charge gradient causes a conformational change in many Na+ channels, allowing lots of Na+ to rush into the cell, generating the all or none response known as an action potential.