In this video I go into more detail on pain perception. First I discuss the importance of pain as a signal of danger or harm to the body. Next I explain the two types of nerve fibers which carry different pain messages: A-delta fibers for sharp, intense pains and C-fibers for dull, throbbing pains. I provide a mnemonic for remembering the fiber types and then discuss two other concepts related to pain: gate control theory and referred pain.

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Video Transcript:

Hi, I’m Michael Corayer and this is Psych Exam Review. In this video I want to go into more detail on pain perception.

In the last video on touch, I mentioned that in our skin we have these things called nocireceptors or nocicepters and these detect pain messages. These are present not just in our skin but in other areas of our body as well. They’re around our organs and our bones and they help to tell us when something’s wrong.

So you might think it would be great to have a pain-free life where you didn’t experience pain at all but actually this would be a very bad situation and there are people who are born with a congenital insensitivity to pain.

Unfortunately they tend not to live very long and this is because their injuries accumulate. They don’t realize that they’re hurting themselves in certain situations. For instance if you touch a hot stove you immediately pull your hand and it hurts but this is to change your behavior as quickly as possible because you’re causing damage to your hand and you don’t want to continue doing that.

You can imagine if you didn’t get that message you might worsen the burn that you’d get on your had. The same would apply to other situations, if you’re stretching a muscle you feel a point where it hurts and that tells you that’s where you should stop stretching it. But you can imagine if you didn’t get that message, you might continue stretching beyond the muscle’s capability and end up tearing it.

Or if you twisted your ankle let’s say and you’re walking. This hurts and this tells you that you need to rest and maybe take the weight off of that joint and allow it to heal. But if you didn’t get that pain message you might not even know there’s a problem and you’d continue trying to walk on it and you’d end up worsening the injury.

So this is what is really important. It also applies to things like infections. So when we get sick, we experiences some, usually some dull throbbing pain and this tells us that there’s an infection or that there’s something wrong and we need to rest, we need to recover or maybe we need to see a doctor and investigate this situation.

But pain is the important message that tells us to do that. So without pain we’d really have a difficult time knowing when we need to change our behavior. Although pain may be unpleasant, it’s a crucial, essential part of life.

Pain messages vary and they can be carried on different types of fibers so there’s two main pain receptor types. The first of these is A-delta fibers and A-delta fighters carry pain messages which are sharp intense kinds of pain. This is like the stabbing sort of pain that jolts you suddenly. So if you get a paper cut on your hand, it hurts very intensely, very quickly, it’s very fast. That type of message is carried on A-delta fibers.

We also have a type of pain receptors called C-fibers. C-fibers carry a different type of pain, they carry the pain that’s a bit slower, it’s kind of a dull, throbbing pain so it’s less intense. but it’s usually longer lasting. Part of the reason this throbbing pain is slow and sort of dull is that it’s carried on unmyelinated fibers.

So C-fibers don’t have myelin on them. If you remember when we learned about neurons, we talked about the idea that myelin speeds up the messages that neurons can carry. In this case, C-fibers aren’t myelinated, so that means they’re going to convey their messages more slowly. So how can we remember the difference between A-delta fibers and C-fibers and the types of pain that they convey?

I have a silly mnemonic for you but hopefully it will help you. Let’s have two people here, not the most accurate looking people but OK let’s have this first person here experience some sharp intense pain. We’re going to do this by stabbing this person and we’re going to stab him with the sharp end of a letter A. See that, it’s a letter A being stabbed into this person and this would obviously cause very sharp intense pain and it would be carried on A-delta fibers. Hopefully that can help you to remember that.

Now over here we’ve got this guy with a mysteriously small head here, and we’re going to give him an aching pain, a dull throbbing pain in his shoulder. And we’re going to express that with this sort of radiating pain coming out of his shoulder. We’re going to draw that with a bunch of Cs. That will hopefully remind you that C-fibers are the ones that carry this dull, throbbing, aching type of pain.

There’s two other theories of pain that you should be familiar with. One of these you actually already know about, you just might not know what it’s called. This is called gate control theory.

So the idea of gate control theory is that our pain messages need to get up to our brain through the spinal cord and they’re sort of competing with other messages that also need to travel along some neurons and get to the spinal cord and brain. Then it’s kind of like a limited amount of bandwidth that we have for getting up there. So the idea is that if we stimulate lots of other receptors non-pain receptors around the area that’s in pain, we can actually reduce the pain message we can inhibit the signal from those nocireceptors.

I said you already know this and I said that because you probably do something like this when you get hurt. So if you stub your toe, your immediate reaction after is to rub your toe. That’s not healing anything, what’s that doing? What it’s doing is it’s sending lots of sensory messages from the toe up the spinal cord. You have now, instead of just the pain message, you’ve got lots of other messages trying to get up the spinal cord there and they’re going to inhibit the pain message. They’re actually going to reduce the intensity of it.

So gate control theory is this idea that we can close the gate on pain messages. Right so this is the idea that we can inhibit pain, pain messages, by stimulating other receptors, non-pain receptors. So that’s called gate control theory.

A final theory related to pain is the idea of referred pain.So the idea of referred pain is that these receptors all have to get to the spinal cord and there are some places where they kind of overlap and there can be a little bit of confusion about where a pain message is coming from. So the idea of referred pain is that the experience of pain can occur in places where it’s actually not where the pain is coming from.
So, experience pain in other areas, meaning in areas where the pain is not originating from. For instance, if you’d have some stomach pains, right? There’s pain receptors around your internal organs and in some cases you might have some pain that’s coming from inside but it almost feels like it’s on the surface of your stomach.

You’ve probably experienced that at some point. It feels like the pain is right here, but it’s actually something that’s happening underneath, inside but because when that message gets to the spinal cord and goes up to the brain there’s a bit of confusion. The pain becomes referred, it seems like it’s coming from one place but it’s actually coming from another and perhaps the most famous example of this, the one that everybody is familiar with is one of the symptoms of having a heart attack.

You’ve probably heard that a symptom of having a heart attack is shooting pains in the left arm. What’s that about? There’s no damage actually occurring to the left arm but what’s happening is the pain receptors inside the chest are sending their message but it feels like it’s coming from the left arm because there’s some overlap where the neurons meet the spinal cord. So that’s another example of referred pain.

OK so those are some theories related to pain. I hope you found this helpful, if so please like the video and subscribe to the channel for more.

Thanks for watching!