Updated: Jul 11, 2019
How acute (or normal) pain works, and why it’s part of our human experience.
This is the first installation in the Pain Science column, and we’re going to talk a little bit here at the outset about how pain is ‘supposed to work.’ Eventually we’ll be adding some instructional videos to the site from various lectures I’ve given over the past few years but many of those are aimed at a graduate school or even postgraduate-level audience and so I’d like to present things here from a more basic level, building up your understanding of pain biology step by step.
Again, as they say, knowledge is power and we want you to be as empowered as possible. Knowledge also alleviates a lot of anxiety, which in the context of pain is frequently worse than the pain itself. At best, anxiety sure does make pain worse (and in chronic pain, often causes pain.)
Getting our heads around the fact that pain is a normal (and even beneficial) part of life is THE first step to containing it, or relegating it to its proper place.
There are two foundational things we’re going to focus on in this post:
· Why we have pain, and
· How it works in the normal or ‘acute’ setting.
It’s important to understand again that we’re beginning the discussion with an explanation of the how and why of acute pain.
Acute means now (or recent) in medical terms, and the standard medical definition of acute pain is that which lasts three months or less. For our purposes here though, I want to re-define acute pain not so much by time (although that's certainly a key aspect), but by normalcy. Getting our heads around the fact that pain is a normal (and even beneficial) part of life is THE first step to containing it, or relegating it to its proper place. Let me re-state it as clearly as I can: pain is a normal part of life
DANGER, WILL ROBINSON.
For those who don't remember the original (or haven't seen Netflix' excellent remake) TV series 'Lost in Space,' Will's guardian robot utters warnings whenever the boy (or the family) is about to encounter... danger.
Several times a week I ask a new patient, "Do you know what the most protective sense we humans own is?" Usually I get a blank stare or some mumbling; the most common intelligible answer I get is "I don't know, touch maybe?"
"Close," I respond. "It sure isn't sight, or hearing, right? Hellen Keller lived to almost 90. Did you know that children born without the ability to feel pain - what we call congenital insensitivity to pain - usually don't make it to double digits?" As I go on to explain to them, pain tells us to get our hand off the hot stove before critical nerves and other delicate mechanisms are destroyed by burn injury. It tells us to go to the emergency room when our appendix is inflamed and nearing rupture. The unfortunate children who can't sense pain sustain the same traumatic injuries, infections and other life-threatening issues the rest of us do, but they don't know about it. They don't call attention to the problem or ask for help, because they lack the guardian of pain.
As my colleague and friend Dr. Beth Darnall likes to say, we’ve been given an efficient ‘Harm Alarm.’ As one of the world's foremost pain psychologists and researchers, taking some time to hear her approach to helping people incorporate a healthy understanding of pain is well worth your time if you struggle with pain. (just Google "YouTube Beth Darnall" and you'll find a dozen helpful videos.)
It's a Two-Way Street
Just like any good conversation, there should be... conversation. Pain is a message to the brain (and depending on how distracted the brain is, like any person, sometimes communicator #1 needs to speak up to get its attention.)
Communicator #1 / Conversation Starter:
"Houston, we have a problem!"
The conversation starts with a message from what we call a peripheral sensory nerve, and specifically these are labeled 'primary (or first order) afferents.' Afferent means that communication is going towards the brain. To complicate matters a bit, sometimes people call these nerves 'nociceptors;' here we'll refer to them as Communicator #1.
Communicator #1 has three parts actually in series - you guessed it: primary, secondary and tertiary afferents. The surface end of Communicator #1 is designed to respond to a specific damaging stimulus, whether crush, cut, heat, cold, chemical, etc. The other end of Communicator #1 goes all the way to the spinal cord, where it relays its message to the secondary afferent by means of a baton - what we call a neurotransmitter (in this case usually glutamate or Substance P.)
You've already guessed it : the secondary afferent does the exact same thing, handing off its baton to the tertiary or third order afferent, usually in a part of the brain called the thalamus. The tertiary afferent then relays the message to the part(s) of the brain that need to hear it, which for the most part live in the cerebral cortex.
Communicator #2 : Response
"10-4, Good Buddy." OR... "Enough already, I heard you!"
Like a conversation, pain by definition doesn't begin until the recipient acknowledges the message and responds one way or another. The brain / Communicator #2 has a variety of options, and usually chooses more than one, often dependent upon nuances of the situation as well as its own habits. Usually the brain responds to Communicator #1 with one of two messages :
"Got it- thanks. You don't have to transmit any more. Communicator #2 out."
OR, some version of the following:
"Eh? Can't hear you - speak up?" / "I'm so sorry to hear it. Please tell me more..."
(We're not really going to pick up these second threads involving continuation of the dialogue in this post, as they have more to do with what we call pathologic pain, or chronic pain. We'll address it later.)
Communicator #2 also usually includes other people in the conversation (very important participants that have to do with learning from the experience, and also more emotional participants - we generally refer to these players as the limbic system.) It's crucial - not just from an academic standpoint, but from a pain management standpoint, I believe - to understand that pain doesn't begin until the brain (Communicator #2) receives the message. It's even more crucial to understand that what we make of the pain, whether it becomes a persistent problem, etc. has to do with all parties to the conversation but primarily these third parties in the limbic system. We'll talk a lot more about that in the future.
Inflammation & Healing/Resolution
Although it doesn't really play into the conversation proper, the site of injury will undergo a (temporary, in health) period of inflammation, whereby defense mechanisms designed to fight off infection and speed healing become active and result in familiar symptoms of pain, swelling sometimes, redness, heat, etc.
It affects the conversation in that Communicator #1 becomes much more talkative/repetitive so long as the inflammation is doing its thing.
End of the Conversation : Modulation
In a state of good physical and mental/emotional health, Communicator #2 (the brain) is able to keep its neighbors (e.g., the limbic system) out of the conversation, and quiet down Communicator #1 with reassurance.
This is called modulation (sometimes 'descending modulation') and for those who are really interested, one of the main ways it occurs is by interfering with baton handoff between the primary and secondary afferents within Communicator #1.
That's a lot, for sure. But understanding the basics of how the system works is very important in understanding what goes wrong in chronic pain, and how we can harness the key players in the system (and other bystanders) to overcome chronic pain, and/or move beyond it. That's of course the point of this whole site.
So in summary,
1. Pain is normal.
2. Pain is vitally important and protective.
3. Pain is a conversation between Communicator #1 and Communicator #2.
4. The more participants in the conversation, the messier it gets. Training Communicator #2 to use discretion and NOT involve more parties is one of the key strategies (with numerous tactical opportunities) in dealing with chronic pain.
Next time we'll talk about how Communicator #1 gets a bit overbearing in chronic or pathologic pain, and how we can learn to correct it. For now, practice telling yourself, "This is all part of a normal process that's in my best interest." Remember: Knowledge is Power.
-Heath McAnally, MD, MSPH
24 Aug 2018
Content on beyondpain.us is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.