Action potential
1st resting potential: -70mV
Intracellular space (negative)
Extracellular space (positive)
Threshold value: -55mV
2nd threshold
when an incoming stimulus causes a change in membrane potential to -55mV action
potential occurs. (all or nothing!)
3. depolarization
Incoming stimuli change membrane potential (-55mV). Voltage-gated Na+ and K+ channels
are activated, with K+ channels opening 1-3miliseconds later. Na+ channels open
immediately due to the chemical gradient and Na+ ions flow into the negatively charged
intracellular space. The negative space becomes more and more positive and more Na+
channels open. This shifts the membrane potential even further into the positive until the
inner space is more positive than the extracellular space. After 1-3miliseconds the channels
then close again.
4th repolarization:
The K+ channels open and the K+ ions flow from the inside to the outside as the outside
concentration is lower and the electrical potential is more negative. This causes the
membrane potential to become low again, but the K+ channels close more slowly and thus
the value goes above that of the resting potential, up to (-80mV).
5. hyperpolarization
I.e. the cell interior becomes even more negative (-80mV) after 1-2 seconds the rest potential
is restored, the channels are closed and a new action potential can be generated.