Pain is one of those “you know it when you feel it” kinds of sensations. But it’s also a strange phenomenon, when you really think about it. A snowball is cold, and so it feels cold when you touch it. A fuzzy pillow is soft, so it feels soft when you touch it. But a knife isn’t painful on its own. Neither is a pot of boiling water or the corner of the chest at the foot of your bed. We handle these things safely all the time, and experience their mass and temperature and texture. Pain exists only in the body, and even more specifically- in our minds… but that doesn’t make it less real! So what exactly is happening when we feel pain, and how do we stop it from negatively impacting our lives?
How does pain work?
Nociceptive pain a.k.a “tissue pain”
There are many different kinds of sense receptors in the body. Some are sensitive to heat or cold, some to touch or pressure. Others, called free nerve endings, aren’t specialized for any one type of stimulus. When a significant stimulus triggers these nerve endings, it sends a message along the spinal cord and up to the brain indicating that something potentially dangerous has happened. The brain then decides (without consulting the part involved in conscious thought, alas!) whether this is something to ignore or brush off… or if it seems likely that damage has occurred. The brain then sends this message back down the spinal cord to the affected part of the body.
If the message is “No biggie, ‘tis but a scratch,” then you’ll most likely shake yourself off and forget the incident even happened. If it’s “WHOA NELLY, THIS SEEMS LIKE A PROBLEM,” then you experience this as pain.
This is useful! Just ask someone with CIPA, or congenital insensitivity to pain with anhidrosis, a disease that leaves people insensitive to pain. Imagine not noticing a bit of grit in your eye until it damages your cornea or developing stress fractures in your feet because nothing is telling you it’s time to sit down, or ending up with burns in your mouth and throat because you don’t realize your deep dish pizza is scalding hot. Pain stops us from trying to walk on a sprained ankle or go for a run when we have a fever. Tissue damage, high temperatures, low pH, and capsaicin (the active ingredient in hot peppers) are all common triggers for this process.
But brains aren’t always correct when it comes to assessing danger. Lorimer Moseley gives a brilliant example of this in his TEDx talk. What’s the difference between the pain from a scratch on the leg and the pain from a nearly-fatal snake bite? Spoiler: it’s whatever your brain is expecting. That’s why you might feel little pain after a bicycle accident, but be in agony when getting the wound stitched up two hours later. Pain is weird.
Neuropathic pain a.k.a “nerve pain”
This is pain that results from an issue with the nervous system itself, rather than surrounding tissues. If you’ve ever banged your funny bone, you know this feeling well. Common forms of neuropathic pain include:
Sciatica: pain in the sciatic nerve running through the hip and down into the leg and foot
Diabetic neuropathy: nerve damage resulting from fluctuating blood sugar levels
Carpal tunnel syndrome: pain resulting from the compression of the nerves that run through the wrist into the hand