Sean Mackey, M.D., Ph.D.
speaker
373 appearances
1 recordings
1 series
first heard Apr 2025
last heard Apr 2025
Sean Mackey, M.D., Ph.D.’s voice in public audio — every appearance, attributed to the second.
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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.
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.
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.
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.
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.
Yeah, yeah.
Yes. I believe firmly it is, and I'm a recovering anesthesiologist. I haven't done it now in... Oh gosh, 20 years. But when I did it, and when you were operating on a patient, the patient is unconscious. They are not experiencing pain. You need a conscious brain for the experience of pain.
Now what people incorrectly made the leap of is thinking, well, they're not experiencing pain, so everything's okay. That would be a logical fallacy because all those signals are still coming from the body. still hitting the spinal cord and having their impact there, all those injury signals, because let's face it, when you do surgery, it's really nothing more than a controlled injury.
We still are trying to unlock the whole consciousness aspect of things, but we're inching our way there. But it wasn't enough to give that.
Exactly. Muscle relaxation.
Part of the challenge was, and now I'm starting to step outside of my wheelhouse, even though I was a member of the anesthesia tribe for a long time, is the levels of volatile gas anesthetic that you need to necessarily obliterate reflexes and full nociceptive impulses would be so high that it would depress one's blood pressure. And so you augment that with an opioid. Understood.
like fentanyl, like morphine, like whatever, and you combine those together, and that's why what the anesthesiologists do is quite magical.
They're working synergistically, and they're working at different mechanisms. Got it. And during that process, the patient is not feeling pain, If they're unconscious, because you do need a conscious, working, aware brain to feel pain, but all of the electrical impulses coming in from the body that are slamming into the spinal cord and the brain are open full bore.
They're impinging on all those brain systems responsible for stress responses.
Yes. And in response to nociception. independent of perception of pain. Right. And you notice that I'm trying to be precise in my language here, because since they're unconscious, there's no pain, but there's plenty of nociception.
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