welcome to anatomy and physiology at Glen Oaks Community College, I'm Dr Ren Hartung
for this video I'm going to talk about the bare-bones basics of membrane potentials
so, what is membrane potential on this is drawing is supposed to
represent a cell a human cell here's the cell membrane the outermost part of
a cell and that's where the action is when we're talking about membrane potentials
and there of course is the nucleus is to show you that this is a cell
when we're talking about a membrane potentials here's the basics of what we mean
there's a charge across this outside memory in a literal electrical charge it
a little bit more positive on the outside a little bit more negative on the inside
by the way when these are reported in your textbook for example
we're measuring from the inside so resting membrane potential is almost always
reported as a negative number because we're measuring relative to what's
happening on the inside. To understand the basics of how this kind of charge
difference works a good first step is to make sure you understand how the cell
membrane is made up so let's take a quick look at the structure of the cell membrane
if I took a little piece of the cell membrane and blew it up a lot
this is what we think we would see these little structures and by the way
let me grab one of them and draw it large or larger --- these are called phospholipids
They have a phosphate head group and that phosphate headgroup likes water
it's attracted to water water easily associated with it --- its hydrophilic
in other words, that's the term for that hydrophilic, whereas the tales down here
they don't like water their made out of lipids and lipids don't have polarity or charged so they
actually don't like water they tend to stay away from water that's the
phospholipid and those are the characteristics that matter
in terms of why they associate the way that they do and cell membranes so let's
get back to the membrane structure
phosphate head group, lipid tales -- and I if I kept drawing this thousands and thousands of times you can
imagine that I can go all around my cell membrane here and that's what this is
made out of but of course we don't draw it that way because doing that would take forever
what this creates in terms of a barrier in terms of a semi permeable barrier
these phospholipids in the way they associate with each other, it's called
a phospholipid bilayer that creates a lipid barrier these tales hanging out
with each other creates a lipid barrier so that molecules that are polar or
charged particles that are polar or charged they can't get through this
barrier easily, proteins are required in the membrane to allow things like this
to pass through. So, for example the two major ions for membrane potential
sodium and potassium -- this cell membrane if it was only made out of phospholipids these guys
wouldn't be able to get through they'd just bounce right off and they would stay either
outside the cell or inside the cell they wouldn't be able to pass across this membrane
again, understand the structure of the cell membrane and in what way it's a barrier
is the beginnings to understanding membrane potential
let's move on from that -- you understand the cell membrane the next step to go to is remember
I said that in order for these guys to get through there need to be proteins
the two major proteins for setting up membrane potential the first one is
called the sodium potassium pump (Na+/K+ pump) it literally pumps sodium and potassium
across the membrane in order to do that it requires energy -- and of course the
energy currency inside of the cell is ATP this protein is gonna take that ATP and
break off one of the phosphate groups turning it from an adenosine triphosphate
into adenosine diphosphate or ADP and then of course we'll have that phosphate group (which by
the way is negatively charged) the energy from removing the phosphate group is
used to do this to pump out three sodiums and at the same time to pump in two potassiums
to pump out three sodium ions, and to pump in two potassium ions
This creates a difference in concentration of course of sodium on the outside of the cell
and potassium on the inside of the cell
There's more potassium on the inside of the cell
less potassium on the outside and there's more sodium on the outside of
the cell less sodium on the inside --- it's important to get that concentration difference,
connect that with your understanding of diffusion because when
we talked about how these potentials can change that comes in real handy
just in terms of charge though, cuz remember what we're trying to do here is
explained how it is that the cell is positive on the outside
negative on the inside, part of this is explained here at least a little bit
just in terms of our accounting of charges notice that the sodium potassium pump
has pumped out three positive charges and while it has pumped in positive charges
as well it's only pumped in two positive charges --- so we already have a
more positive charge on the outside
less positive charge on the inside you've got a piece of the negativity going on here
in other words, the inside of the cell just talking about sodium potassium pump
is a little bit more negative because it has fewer positive charges
let's go to the next protein -- this next protein is called the potassium leak
channel and it does exactly what its name says,
it literally allows potassium to leak out
remember that's what we were pumping in over here.
So, the sodium potassium pump pumped out some positive charge
it pumped out more positive charge than it pumped in, and now
those positive charges that the sodium potassium pump pumped, we're allowing some of those
to get out, thus increasing even more
the positive charge on the outside and decreasing the positive charge or
increasing the negative charges on the inside
these two proteins that I've just described
those are the two major proteins for setting up resting membrane potential
they set it up and they maintain it and again that's why the cell
is positive me outside in negative on the inside
and that is the bare-bones
basics of membrane potential --- other things to mention there are other ions that influence
membrane potential calcium ions can influence membrane potential for example
chloride ions can influence membrane potential basically any charged ion can
influence membrane potential --- calcium ions are important in in terms of the
membrane potential changes that cardiac myocytes your heart cells undergo
chloride ions with their negative charge they're important for some of the
membrane potential changes
that occur in neurons. So, while sodium and potassium ions are the major ones
involved with membrane potentials I don't want you to think that the only ones
these aren't the only ones either any charged ion can have an influence on it
potentially at least, because I don't want to risk going too far and giving you too much information right now
that's the bare bones basics of membrane potential so quick quiz to make sure
your paying somewhat attention to this, I'll erase your helpers here
just at the bare bones basics what are we talking about when we say membrane potential?
And of course the answer to that is we're talking about the difference in
charge across a cell membrane and for most cells that charge is a little
bit positive on the outside and little more negative on the inside
What are the two major proteins involved with setting up membrane potential?
And the answer to that is the sodium potassium pump and the potassium leak channel
Let's continue with those two channels.
What does the sodium potassium pump do and how does it do it?
And the answer to that is a little bit more involved, but it's still pretty simple.
to be honest, if you can draw this same picture that I drew earlier
ATP being broken broken down into ADP plus P
and then that energy from the ATP being used to pump out three sodium ions and pump in two potassium ions
if you can reproduce this picture for yourself
that will answer almost any question you might get about the sodium potassium pump
and I'm assuming you're not graduate school and learning about its protein structure all
these things but just bare bones basics for understanding sodium potassium and
this is a great one to know because it comes up over and over again it's it's
used a lot in living cells so that's the sodium potassium pump our next question
What's the other protein involved with resting membrane potential or with
setting up membrane potentials?
And the answer to that one, and we already did it... it's the potassium leak channel. So what does it do?
And the answer to that is... I drew it over here and again you can just remembered simply as a drawing
it allows potassium to leak out of the cell
confused and which direction the potassium is going to move remember that
this is simply a channel it's just open so the potassium is going to move
according to diffusion and remember the sodium potassium pump fist pumping
potassium in so there's going to be a higher concentration of potassium in
here therefore the potassium is going to defuse out of the cell from an area where
potassium is a higher concentration to an area where potassium is it a lower concentration
by the way for those of you who are learning anatomy and
physiology now you may have had biology classes in the past and you might be
getting bells rung in your head because you're like "Oh, I think we this in Biology a little bit"
These kinds of things, understanding diffusion understanding the cell membrane and understanding proteins
in the cell membrane and how they basically function to me those are like
the basics of understanding human biology and general or anatomy and
physiology in general we could even go back to chemistry in terms of
understanding what we did what we mean when we say hydrophobic and hydrophilic
and what kinds of things like water and what kinds of things don't like water so
anyway, those basics should always be there you should practice and memorize them
because they'll come in handy even later on when you're helping with patients and
things like that if you're going into the medical field
alright, I'll get off my high horse
thank you once again for watching and as always if you have any
questions please feel free to leave them in the comments down below