Pain science! - nociception
In my studies so far (all 4 weeks worth) I've encountered a lot more talk about pain than I expected. This is because there is a lot more going on with pain than we think. For example, did you know that pain is the number one reason that people seek treatment? Or that people can feel pain in limbs that aren't even theirs? Or that pain can be felt without any physical stimulus whatsoever? Pain science is a fascinating field and that's why today I'm going to be talking about pain and nociception.
Let's get started with some definitions.
Pain is the unpleasant sensory and emotional experience that is associated with tissue damage.
Nociception is the bodily process of sending messages to the brain about potentially harmful stimuli.
Just like the thermoreceptors in your skin that send messages to your brain when they touch something hot, there are nociceptors in the cells around your body that will send a message when they percieve there is a potentially harmful stimulus (called a noxious stimulus).
For example the nociceptors might say:
"There's something scraping against your ankle"
Your brain then interprets this message using past and learnt experiences.
"Have I felt this before? Yes, I brush against harmless twigs all the time when walking"
Then, as the output of this process, you feel the pain.
"just a little scratch, nothing too painful"
It could be a snake bite for all you know, but your brain does the best it can given the information that it has in order to protect you. Pain is a natural instinct designed for survival.
Pain does not always mean there is damage to the tissues.
Pain can be severely altered based on a variety of factors, more than I have time to list!
Past experiences are heavily called on to interpret what the nociceptive signal means.
"There's something against your ankle" "Felt this before? Yes it was a snake bite, I almost died!" "Searing agony, absolute 10/10 pain." Then you look down, "oh it's just a twig"
Mood, stress and sleep are other factors that affect your experience of pain. If you're feeling stressed out, losing sleep and "having a bad day", your threshold to feeling pain will be far lower than normal.
Your body can also learn to create pain from stimuli that usually isn't painful (a non-noxious stimulus). This is called allodynia. If you've ever gently brushed the skin around a recent cut and felt pain, you've experienced allodynia.
Pain can also be enhanced by a process known as sensitisation. This is where the same level of stimulus begins creating more pain. This process is super important when beginning to understand the factors behind chronic (long term) pain.
There are two types of sensitisation: central and peripheral sensitisation.
The best way to describe this is in terms of a microphone on a laptop used for an online meeting, because over the last 12 months we've all become far more familiar with these than we would have liked!
The microphone is like the nociceptors, it picks up the stimulus of you talking (a dangerous substance) and converts it into electrical signals in order to send it to the computer (or the brain*).
*and spinal cord but let's keep things simple here, it's all part of the central nervous system so I'm going to just use the word brain to refer to where the signal gets processed.
Central sensitisation is when the brain takes these signals from the microphone and starts boosting them. In a meeting this would make your microphone louder, but in terms of pain, it increases that too. This happens when the body gets used to sending out pain signals such as in long-term back pain, resulting in that same pain getting worse despite no difference in the condition.
Peripheral sensitisation is when the nociceptors (microphone) begins sending signals at a lower threshold. There is usually a setting for online meetings where you can slide this bar up or down to make sure your microphone doesn't activate for a background noise. In humans, this means there are more signals being sent to the brain telling it there is a noxious stimulus.
An example of a microphone sensitivity slider. Peripheral sensitisation occurs when the white bar slides to the left, meaning that even smaller sounds (or stimuli) will be picked up and transmitted. If only it was this simple in humans!
Both central and peripheral sensitisation can occur at the same time to increase your perception on pain. This is a common occurrence in chronic injuries.
Watch this short video by Lorrimer Mosley to help your understanding, see how this can happen with problems such as long term back pain, and how we can learn to change things.
So, to summarise, here are the key points I want you to take away from this blog:
Pain does not come from the body, but from the brain - there is a difference between pain and nociception.
Pain does not have to arise from tissue damage.
How you feel pain is influenced by previous experiences as well as mood and other factors.
Pain from a normally gentle stimulus is called allodynia.
Persistent pain can lead to sensitisation, either from the nociceptors (peripheral) or from the brain (central)
For further understanding on the topic you can check out this TedTalk, another video from the well spoken Lorimer Mosley, on why things hurt (LINK) or head to this website to find more useful resources (LINK).
I hope you enjoyed this blog, and if you did, please consider checking out my other posts under the BLOG page.