Voltage-gated Na+ and K+ channels respond to a change in membrane potential.
When a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into the cell.
The movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to open.
A strong stimulus results in a massive change in membrane voltage called an action potential = signal.
Strong depolarizing stimulus
Membrane potential (mV)
(c) Action potential = change in membrane voltage
An action potential occurs if a stimulus causes the membrane voltage to cross a particular threshold.
An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane.
Action potentials are signals that carry information along axons.
A neuron can produce hundreds of action potentials per second.
The frequency of action potentials can reflect the strength of a stimulus.
An action potential can be broken down into a series of stages.
The role of voltage-gated ion channels in the generation of an action potential
Rising phase of the action potential
Falling phase of the action potential
At resting potential
Most voltage-gated Na+ and K+ channels are closed, but some K+ channels (not voltage-gated) are open.
Voltage-gated Na+ channels open first and Na+ flows into the cell.
During the rising phase, the threshold is crossed, and the membrane potential increases.
During the falling phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell.
Cell is now repolarized but is not normal until Na+ K+ pump restores original resting potential.