Sean Mackey, M.D., Ph.D.

Those are your A-delta fibers at 10 meters a second, rapidly getting up to your brain, rapidly putting into play systems to protect yourself from harm. You withdraw. You have a reflex that's occurring in your spinal cord. You're not even consciously aware of it. Your brain is setting into play escape mechanisms. The pain that you experience is sharp. It's well localized.

Those are your A-delta fibers at 10 meters a second, rapidly getting up to your brain, rapidly putting into play systems to protect yourself from harm. You withdraw. You have a reflex that's occurring in your spinal cord. You're not even consciously aware of it. Your brain is setting into play escape mechanisms. The pain that you experience is sharp. It's well localized.

You know exactly where you stepped on that tack. Then about a second, two seconds later, you get this hot burning flooding sensation come over your thumb with you hit it with a hammer. And you think to yourself, oh, damn, this is really going to hurt. And it gets hot. It gets burning. Those are your C-fibers, unmyelinated, slow, getting up to your brain.

You know exactly where you stepped on that tack. Then about a second, two seconds later, you get this hot burning flooding sensation come over your thumb with you hit it with a hammer. And you think to yourself, oh, damn, this is really going to hurt. And it gets hot. It gets burning. Those are your C-fibers, unmyelinated, slow, getting up to your brain.

And what you also notice for the first time is you don't like this. This has an unpleasant quality to it that you didn't get as much with that A-delta sharp pain, but you're getting with those C-fibers. That's really clear.

And what you also notice for the first time is you don't like this. This has an unpleasant quality to it that you didn't get as much with that A-delta sharp pain, but you're getting with those C-fibers. That's really clear.

That's exactly it. And it is synapse, and there are synapses in the ventral or anterior, the front portion of your spinal cord, which is, as you know, your motor part of that spinal cord. They're making synapses, and it's causing a classic withdrawal effect.

That's exactly it. And it is synapse, and there are synapses in the ventral or anterior, the front portion of your spinal cord, which is, as you know, your motor part of that spinal cord. They're making synapses, and it's causing a classic withdrawal effect.

Yeah, they would still feel pain.

Yeah, they would still feel pain.

Those A delta fibers are still- They're still going up. Going up. They're in the spinal cord. They cross over to the other side. So there's an afferent and an efferent to the whole thing. Indeed. Okay. Indeed. We think of these pathways. The main one that we all learn in medical school and we think about is a spinothalamic pathway. This goes from the spine up into your brain.

Those A delta fibers are still- They're still going up. Going up. They're in the spinal cord. They cross over to the other side. So there's an afferent and an efferent to the whole thing. Indeed. Okay. Indeed. We think of these pathways. The main one that we all learn in medical school and we think about is a spinothalamic pathway. This goes from the spine up into your brain.

We're going to get there. But yes, if you had no C-fibers, you would still feel pain. That's one of the other things I think it's important to understand about pain is we've been trying to knock this out for untold years. And we've not been very successful with it. And part of the challenge is pain is so highly conserved from an evolutionary standpoint.

We're going to get there. But yes, if you had no C-fibers, you would still feel pain. That's one of the other things I think it's important to understand about pain is we've been trying to knock this out for untold years. And we've not been very successful with it. And part of the challenge is pain is so highly conserved from an evolutionary standpoint.

As I was alluding to, back to single-cell organisms, reward, pain. We evolved over the years to have this complex experience of pain, but also redundancies. You knock out one pathway related to pain, there's others there. And they find their way up into the brain just about no matter what.

As I was alluding to, back to single-cell organisms, reward, pain. We evolved over the years to have this complex experience of pain, but also redundancies. You knock out one pathway related to pain, there's others there. And they find their way up into the brain just about no matter what.

You could go pretty deep in there, and I get the debate. It's a great debate over wine or beer, and I understand actually taking it seriously and having that debate. A lot of different opinions on this. I actually don't engage in that debate. I think you have to, first of all, define the thing that you're debating. You have to very clearly define the thing.

You could go pretty deep in there, and I get the debate. It's a great debate over wine or beer, and I understand actually taking it seriously and having that debate. A lot of different opinions on this. I actually don't engage in that debate. I think you have to, first of all, define the thing that you're debating. You have to very clearly define the thing.

And in this case, our definition of pain is a rather human experience of pain.

And in this case, our definition of pain is a rather human experience of pain.