00:01
Okay. So let’s take a
closer look at that neuron.
00:04
And we have -- we have a
couple of images here.
00:06
So the first image labeled A
is looking at a longitudinal
cross section of a neuron.
00:12
So it’s a neuron starting going
this way, and we’re looking at.
00:15
And you can see in the middle,
what’s labeled axon is the axon.
00:19
And then we have these kinds of
bubbles that are surrounding it
and that would be the myelin
or that insulating material.
00:24
So, the idea of the myelin is to increase
the conduction of the action potential.
00:30
So increase the conduction speed of the
signal traveling down the neuron.
00:37
Now, think, the analogy I like to use is,
think of an extension cord or a power cord.
00:43
So it has that orange
wrapping on the outside or
whatever color it is and
that’s an insulator.
00:48
So it does two things.
00:49
It prevents you from getting an
unwanted perm and getting electrocuted.
00:53
And it also helps aid in controlling the
conduction of the signal down the power cord.
00:58
So exact same idea here.
01:00
Now, the differences in a neuron,
we actually have little gaps
in the insulation and these are
known as the “Node of Ranvier”.
01:07
And what ends up happening is
the action potential actually travels
from node of Ranvier to node of Ranvier.
01:15
And that exposed
area of insulation,
so there’s a lack of
insulation, that exposed area
so there’s a lack of
insulation, that exposed area
has a high density of those voltage-gated
sodium and potassium channels.
01:28
So what ends up happening is
as there is a voltage change
as the signal travels down the axon, it
activates those voltage-gated ion channels
in that specific area
at the node of Ranvier.
01:38
And so the signal travels there.
01:41
It causes a change in the
internal environment
and that’s -- so you can see -- you can see
these arrows that looked like a cycle,
what they’re showing is that there’s
a voltage change and that shifts
to the next node of Ranvier activating
that node and then it goes node.
01:53
So it’s going node
to node to node
as opposed to having to travelled
on the whole length of the axon.
01:59
So, you can try
this as an analogy.
02:01
Get 20 of your best friends,
hopefully you have 20 friends,
line them all up and take a
piece of paper or a ball.
02:08
And if you were time, --
let’s get actually, let’s get 40
friends and we’re going to get 20.
02:13
So you obviously don’t
have 40 friends.
02:14
So let’s go 10 and 10.
02:16
Ten friends, ten friends
and align side by side.
02:19
One group of friends
gets a tennis ball.
02:21
The other one gets
a tennis ball.
02:22
And their job is to take
the ball and pass it
to the person behind them
and you keep passing.
02:26
And you’re going to time one group that
does each person gets to see the ball.
02:32
The other group of friends,
you’re going to pass the
ball but they’re going to
pass to every third person,
and you can have a
race to see who --
how long it takes to get the
ball to the last person.
02:41
Who do you think is
going to win that race?
Obviously, the group or the ball
skipping every third person,
the ball is going to get
there very, very quickly.
02:50
So you’re tossing it, you’re
tossing it, you’re tossing it,
boom, boom, boom, you’re
done versus here.
02:55
You take it, no, no, you
take it, no, you take it.
02:57
And so, the process of jumping allows
it to actually expedite or speed up
how quickly you can send that
signal down the length of an axon.
03:05
So now we have another image that shows
two neurons, one on top of each other.
03:08
One on the top is unmyelinated,
meaning there’s no insulation
and so it’s going to
have to travel down the
whole length of the axon.
03:15
And the one below is
comparing how there’s --
those node of Ranvier and it’s
jumping from node to node to node.
03:21
That idea being that it is much
faster when you have these gaps.
03:25
Okay. So, sort of the
summary to take home is
myelin equals node of Ranvier, which
means faster speed of conduction.
03:32
That process of jumping is
called “saltatory conduction”.