What is pain and why does it hurt?! In trying to think of the easiest way to explain this, I thought it best to first learn a bit of neuroanatomy. I’ll try and keep it simple and painless (admit it, that’s funny). You can divide our nervous system into two separate regions: The central nervous system - brain, brain stem, spinal cord; and the peripheral nervous system - all the nerves that leave the spinal cord and innervate everything in our bodies. We also have an enteric nervous system, which controls our digestive tract, but let’s save that for another day.
Still with me? Great. When we encounter an unpleasant stimulus, we convert it into an electrical signal, which gets sent via the peripheral nervous system to the spinal cord, and ultimately to the brain for processing. Let’s use the example of poking yourself with a sharp object. If you poke lightly, it likely won’t hurt. However, if you keep applying pressure you will feel pain, and the harder you press the more pain you’ll feel. The things that sense pain, are called the peripheral nociceptors. These, like all nerves, operate on an all or nothing principle. This means, that there is a threshold where if a stimulus isn’t strong enough, it won’t cause the nerve to fire. However, if the stimulus is strong enough, the nerve will fire, and once it does it cannot be stopped. As the stimulus gets even stronger, more and more peripheral nociceptors reach their threshold and send their electrical impulse to the spinal cord.
Once in the spinal cord, the signal must travel upwards to reach the brain for processing. If you look at the spinal cord in cross-section, it’ll look like a mushy round grey thing with a darker grey butterfly shaped thing in the middle. But if you look at a textbook image, someone has carefully coloured in and labeled the different “tracts”. You can think of the spinal cord as a wiring harness. Each wire in the harness would be a tract, carrying information to a certain part of the computer, or brain in our case. This allows everything to remain relatively organized. Pain signals are carried through the spinothalamic tract. That probably doesn’t mean anything to you, but don’t worry about it.
We still good? Okay, I’m going to throw some big words at you, but fear not, it’ll all come together at the end. The pain signals travel up the spinothalamic tract to reach the thalamus. The thalamus is basically an operator that sends signals where they need to go in the brain. The signals are then sent to various regions of the brain (including the amygdala, hypothalamus, basal ganglia, periaqueductal grey matter, the insula, and the anterior cingulate cortex, if you were curious).
Finally, when the signals reach the areas mentioned above our brains interpret the signal as pain. Something that is very interesting (to me at least) is that while most of the time nociceptive signals are subjectively interpreted as pain, sometimes we can dissociate the pain signal from the experience of pain. In other words, the signal can be sent without us registering it as painful, and pain can occur in the absence of a noxious stimuli. This phenomenon can be seen in instances of massive trauma (like a car accident) when, despite a severe injury, someone exhibits a painless state, and conversely, when individuals with functional pain syndromes report considerable pain in spite of having no observable tissue damage.
Keep an eye out for a future post where we’ll discuss how we can influence pain! In the meantime, if you’re in pain do yourself a favour and give us a call. We’ll help you figure out what is going on, and we’ll get you back to being you!
Dr. Lee Brotherston
Partner and Chiropractor at
Oak Ridges Health Group
58 Brock Street W, Suite 201
Uxbridge ON, L9P 1P3