Okay. Let’s move on to our
next type of channel.
These are ion channels.
Ions channels are going
to be pretty selective
to only allow certain
ions to transport across.
The prototype that we’re
going to use is going
to be the nicotinic
But for ion channels to work, you need to
make sure you have a concentration gradient.
That concentration gradient can be
established by another type of transporter
such as a pump or you take
advantage of that ion difference
between inside the cell
and outside the cell.
There is usually a limited amount
of time that an ion channel is open
and it usually requires some sort
of activation type of process.
But this activation type of process can be
varied, but it hints on the ion channel.
Some of them are voltage-gated,
which means there needs to be
a small electrical potential
difference across that cell membrane.
A great example of this is in
nerves, where you have sodium
and potassium channels
opening and closing,
but they won’t open and
close until there’s enough
of an electrical difference across
that membrane of the nerve.
Other types of channels
This means that they need a
specific signal to open.
Sometimes it only involves one
ligand, sometimes it involves two.
But besides voltage and ligand-gated
channels, there a few others.
Some of the different cells that
you have respond to stretch,
some respond to
So there are other ways
to open up ion channels,
but the two main ones are
voltage-gated and ligand-gated.
Our prototype, the nicotinic
will use a ligand-gated
The other thing about ion channels
that we always have to keep in mind
is usually there’s a
selectivity filter in them,
and this allows for only
then one or a few selected
types of ions to move
through at any one time.
So, you have sodium channels,
you have potassium channels,
you have calcium channels,
you have chloride channels,
and only every now and then,
we have a non-selective,
for example positive or
cation channel occur.
So let’s go to our
This is the nicotinic
and this is very important
certain types of cell
signals and certain ions.
You need two ligands to bind and
these are two acetylcholines
that will bind to the portion
of the acetylcholine receptor.
By both binding,
it will open up that
and therefore, allow ions
to travel through it.
In fact, though this is very selective
to only allow positive ions to pass.
Now which positive
ions are going to pass?
In this case, we
have three choices.
Is it going to be calcium, is it going to
be sodium, is it going to be potassium?
For this, you have to think back
in to how these are partitioned.
If you have a gradient across that
cell membrane, you will be able to
answer that primarily sodium will
go across of influx into the cell.
Although there might be a little bit of
calcium, the primary one will be sodium.
It doesn’t work to have
potassium cross because the
concentration gradient is going
in the opposite direction.
So where do you use these channel
and why is it so important?
Well, it is the primary channel
to engage muscle contraction.
So, if your nerves want to
tell your muscles to contract,
you’re going to have to use a
nicotinic acetylcholine receptor,
and this is how your muscles figure out,
oh, my goodness, we need to contract.
It is also very important
in ganglionic function.
And what the ganglia are, are specific aspects
just outside for the autonomic ganglia,
sympathetic chain, just
outside the spinal cord,
or you might have parasympathetic ganglia
that are located closer to an organ.
And these are synapses in
which one nerve stops,
sends a chemical signal to another
nerve so it propagates on,
and these are in certain
spots known as ganglia.
So these nicotinic acetylcholine
receptors are very important
for both neuromuscular function
and nervous system function.