Nervous System: Saltatory Conduction – Biological Bases of Behavior (PSY, BIO)

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”.