Pain is a fascinatingly complex subject.

Knowing more about pain has huge value for those whose job it is to help those in pain.

At the same time, it's also advantageous for those in pain to have some knowledge of what is happening.

Let's cut to the chase, the biggest piece of information we can share with patients is that there are three types of pain. In three posts, we can cover:

• Nociceptive pain
• Neuropathic pain
• Nociplastic pain

Here goes.

The first type of pain you should know about.

Nociceptive pain is the sort of pain you’re most likely familiar with. It's a warning signal that something isn't right. Life without it would be risky.

The word nociception breaks down to noxious and reception in my mind.

In reality, this starts with nerves all over our body that report noxious signals to us. You’ll notice that I’ve not used the word “pain” yet. Instead, I'm saying noxious, by which I mean sensations that are perhaps unwanted, perhaps unpleasant.

What sensations do we get?

We get different sensations from different types of nerves. You don’t need to know about these types, but it makes sense to tell you that while some nerves tell us about touch and some about temperature, others tell us about vibration, and there are also nerves that report chemical presence.

Each of these “channels” of information can deliver sensations that might be pleasant, a nice warm bath, a light touch. But they can also cross a threshold where their signals become, well, unpleasant. That threshold is an important part of the pain system.

Making sense of what we feel

Nociceptive pain begins with touch, temperature or vibration, or sometimes a chemical input. These inputs are relayed first to our spinal cord, and then to our brain. We’ll skip the spinal cord for now, and instead think about our brains.

When a signal reaches our brain, it is merely information about touch, pressure, temperature, vibration, chemical presence. What we do about that signal depends, at the simplest level, on the strength of the signal.

If you’re testing the temperature of your bathwater, you dip a hand in. Temperature receptors send information to your brain, and your brain makes a decision. A little too hot perhaps, or way too hot. If it’s scorching, your brain fairly quickly makes a decision to withdraw your hand. Sensible.

Sense – measure – decide

This process of “sense – measure – decide” occurs with most things we feel. In most cases, there is a simple threshold where touch or temperature cross a line and switch from acceptable to unacceptable. This is fairly consistent amongst people.

But sometimes this threshold, the decision-making part of the process can be fooled by the presence of other information. It can be raised or lowered.

What if someone told you before you put your hand in bath water that it was nearly boiling. You’d have to wander why you would put your hand in to test it, but that’s another story. For now, let’s imagine that you dip the tips of your fingers in. Knowing that you’ve been told to expect very hot water, you might find that you withdraw your hand as soon as you sense the water, but before any real sense of the temperature - before the signal has been “measured”. On reflection, you then realise that the water is not so hot, you’ve been fooled, you reappraise, and you plop your hand in.

Amplify or subdue

We can be tricked and have our decisions impacted by external influences. While the basic nociceptive basis of pain is based on sensing what is around us, there is also the possibility of an incoming signal being boosted or dampened.

We will look at these processes in more detail when we consider nociplastic pain, but for now, it’s enough to appreciate that our sense of pain can be temporarily adjusted by our expectations, by misjudging things, or by relying on our past experiences of pain.

People who have had terrible pain in the past might get similar sensations from much more minor injuries in the future. Their memory of pain affects how their brain decides to appraise the incoming signals, and an extra layer of pain is heaped on in anticipation of a repeat of the original injury.

In contrast, there are stories of soldiers who report no pain when suffering terrible injuries on the battlefield. Their brains are simply too busy with having to deal with their surroundings to have any time to process the incoming noxious signals, so there is little in the way of a pain response.

In summary

Nociceptive pain starts with a noxious signal somewhere in the body.

It’s relayed to our brain, where there is room for amplification or damping down as it is being appraised.

However much the volume might get turned up or down, there is still a linear relationship between the noxious input and the creation of “pain”. When the input stops, the pain stops.

Up next...

Next time, we’ll look at neuropathic pain. A completely different kettle of fish. 

After that, we can look at nociplastic pain, where some of the processes we've covered here go wrong...