we have membrane potential down, what
do we know that’s most important?
Potassium is very important for
resting membrane potential.
Let’s manipulate it a little bit
because you won’t always have the
same potassium concentrations, right?
There are times when you
have high potassium,
there’s times when you
have low potassium.
How does that change
So if we have our cell here at minus 70,
it’s normally leaking out some potassium.
That’s very normal, sodium-potassium
pump rotates some of it back in.
If you are in a
meaning there’s now low potassium
in the extracellular space,
so that’s the interstitial fluid and
the plasma, have low potassium.
How does this change
More potassium will want to leave the
cell because the concentration gradient
is higher, that hyper polarizes the
cell and makes it more negative.
You can see the more negative
here within oscilloscope tracing.
So what you’re doing is moving
more potassium out of the cell.
It’s getting closer to
this minus 90 value.
If you actually measure it, you
can get all the way to minus 90
in a hypokalemic environment.
What if you start with a membrane
potential that’s normally about minus 70,
you have the normal potassium
leak out of the cell,
and now, instead of hypokalemia,
we’re in hyperkalemia.
We have a high amount of
potassium outside the cell.
This could be for many
It could be because other cells in the body
are pushing its potassium out of the cell,
which sometimes happens
during an acidosis.
It could also be that you have dietarily
intaked more potassium than you need.
So if you’re in a
membrane potential rises.
It becomes less negative.
There is less of a driving force for
potassium to want to lead the cell.
It’s inhibited because the driving
force is not there to the same extent.
So we call that movement from minus
70 to minus 50 a depolarization.
If you haven’t reached
threshold yet, that’s okay.
That’s an action potential.
We’ll get to that soon.
But what you’re doing
If you go from minus 70 to a lower
number, we are hyperpolarizing.
It’s easy to think of these two
values if you look at them on a graph
that uses membrane potential.
Going up is depolarization, going
down is hyperpolarization.
Having a different concentration isn’t the
only thing that affects membrane potential.
Currents can also change
For example, once you open up
channels that were initially closed.
So what we have
We had sodium channels closed,
calcium channels were close,
chloride channels were closed.
What happens if
you open them up?
Membrane potential changes.
So here, this is showing you an example
of opening up a sodium channel
and you can see a large
change in membrane potential
as there’s an inward
flux of sodium.
So sodium influx allows
for a depolarization.
Why? Because it’s Nernst equation
value was around 61 millivolts.
So as it travels in,
membrane potential rises.
How about potassium?
If you opened up even more potassium
channels than what are open at rest,
how would that change
In this case, you would
have a loss of potassium
so that would hyperpolarize
The conductance moves out,
but the voltage goes down.
So you can see how currents
change this whole process.