So we've talked a little bit about the different types of potential.
Creation of an action potential or a graded potential is going to rely
on the fact that the membranes of neurons at rest have what's known as a resting membrane potential.
What does this mean?
First, the membrane is going to be positive outside and negative inside thus, it is polarized.
We establish this through unequal distribution of ions across the membrane
and the selectively permeable membranes to sodium and potassium.
Specifically, there are more potassium leak channels than sodium leak channels
so more potassium is going to leak out of the cell whereas less sodium is leaking into the cell.
At the same time, anions such as chlorine are not able to leave the cell
as there are no leak channels associated with anions.
This is going to further lead to the inside of the cell being more negative than the outside of the cell.
Finally, we have sodium-potassium pumps.
These are energy requiring ATPases that are going to pump 3 sodium molecules out per 2 potassium molecules in.
Therefore, it is a net positive charge out of the cell and again, further polarizes the cell.
Now that we've learned about the polarized plasma membrane of neurons,
let's discuss what happens when we depolarize the membrane making it more positive inside of the cell
instead of the more negative that we have during resting membrane potential.
Deviations from resting membrane potential lead to other potentials.
There are two types: the graded potential and the action potential.
The voltage at a resting membrane potential is usually -70 millivolts.
During a graded potential, we increase the voltage slightly thus, depolarizing the membrane.
A graded potential is going to occur in response
to the opening of either mechanically gated or ligand-gated ion channels.
This causes an influx of positively charged ions back into the cell
which is going to increase the voltage from -70 millivolts to closer to 0 millivolts.
The amplitude or size of a graded potential is going to depend on the strength of the stimulus.
The more or stronger the stimulus that is received, the more the membrane will be depolarized.