There are other ways that cells can
communicate with each other that
don’t involve hormones, and I want
to say a few words about those.
Well, we all know of course
of nerve transmission.
Nerve transmission is a way for one part of
the body to talk to another part of the body.
They have all specialized nerve cells that use ion
gradients and neurotransmitter molecules to transmit
information like, “Hey dummy, you’ve got your finger
in the flame, get the finger out of the flame."
That goes from the end of my finger into
my brain and happens almost instantaneously.
This process can be blocked by
ion channel blocking molecules.
And these often have medicinal purposes, for example,
people who have irregular heartbeats, maybe have part of
their ion channels within their heart blocked by ion channel
blocking proteins to slow down that arrhythmic process.
Another type of non-hormone signaling
that happens inside the body is
that done by the prostanoids, or more
commonly called the prostaglandins.
These molecules are derived from arachidonic acid and you
can see two of them shown in the figure on the right.
They’re derived from arachidonic acid which is a 20 carbon
molecule and they exert their effects
near where they’re released.
They don’t travel very far
because they’re fairly unstable.
There’s a related group of prostaglandin
molecules called the prostacyclins
and another more distantly related group
of molecules called the thromboxanes.
And they all have different effects.
The synthesis of all the prostanoids
however, can be inhibited by steroids.
These steroids include hormones like prednisolone and
non-steroidal anti-inflammatories like aspirin and ibuprofen.
Now, what are they doing?
Well the prostaglandins for example are involved in
pain responses, among other effects that they have.
So when you think of a pain killer, what they’re doing
is they’re inhibiting the production of prostaglandins.
Those prostaglandins acting very
locally in the area they were released.
So for example, if you got stung by a
bee, the sting that you feel associated
with that arises from release of arachidonic
acid at the point of the sting.
Painkillers help to kill the
effects of prostaglandins.
Nerve transmission as I said, is a almost
instantaneous process that happens.
And I want to spend just a
few minutes talking about it.
A cell at rest, a nerve cell at
rest, has a high concentration of
sodium outside of it, and a high
concentration of potassium inside.
That happens as a result of action of a
protein called the sodium potassium ATPase.
That’s a cell membrane protein that pops sodium out and
potassium in, creating what are called ion gradients.
When the nerve cell is stimulated, the
sodium gates of the nerve cell open.
Well if you open the gates, the
flood gates, the flood comes in.
And the flood that comes
in here is sodium.
That change of concentration of sodium from outside
the cell to inside the cell causes a voltage change.
Well sodium is charged.
So when you change the charge difference across
the cell, there’s a voltage associated with that.
And we can see that process
happening in the graph on the right.
The graph on the right shows, at the end
of point one where we see stimulus, we
see an increase in voltage and that increase
in voltage is the sodium coming in.
That change in voltage is
called the action potential.
Well that action potential is a stimulus for
everything else to happen inside that nerve cell.
That action potential actually causes
this potassium gates to wake up and say,
“Hey, there’s too much sodium coming in,
we’ve got too many plus charges coming in.
Let’s get rid of some
of these plus charges".
And since potassium is plus charged,
it goes racing out of the cell.
Well the voltage falls, so we start letting
more positively charged molecules out.
The action potential which rose is now falling
in the process we call repolarisation.
Ultimately, the potassium goes too far and
it undershoots, that’s the recovery part.
We see when it undershoots that
too much potassium went out.
Well at that point,
the gates all close.
And then the sodium potassium ATPase
picks up and reestablishes the gradients.
But why is that important?
Well we started the process at one end
of a nerve cell that gets propagated
all the way along the nerve cell
over and over and over and over,
until it reaches the end of the nerve
cell where a neurotransmitter
continues the same signal from that
first nerve cell to a second one.
Ultimately that pathway
makes its way to the brain.
Now what’s remarkable is to think, that
happens on the order of less than a second.
It’s a pretty phenomenal process.
After this recovery phase has happened for a
nerve cell, the cell is ready to transmit again.
Now we can actually see schematically in this
figure what’s happening with this process.
We see on the left at the bottom that we
see a nerve cell has gotten a stimulus.
And when that stimulus happens, we
have opening of gates that allow
the movement of sodium ions shown in red into the nerve cell.
We actually see that happening
in the second of power over.
We see the sodium gates have opened and
we see the movement of the sodium ions in.
We also see the movement of potassium ions out
because potassium is countering that effect.
Well the result of that mixing of the two is where we started
with a gradient, more sodium out and more potassium in.
We now have a pretty
even mix of the two.
When we take that gradient, what happens is those
ions actually start moving through the nerve cell.
And they move through the nerve cell, and we can
actually see that process happening in the third process over.
We’re now in the middle of the nerve
cell, we see a more even mixture
of the green and the blue dots; the
potassium and the sodium ions.
That nerve potential has moved from the end of
the nerve cell up to the end of that nerve cell.
And when it gets to the end of that nerve
cell, a neurotransmitter is released that now
leaves the first cell, goes to the second
cell and starts the whole process over again.
So this sequential process of letting
ions in and allowing them to move
through a nerve cell is how nerve
signals actually move through our body.