For instance today I removed a mole with excision (cutting it off) at the doctors office with local anaesthesia of course. It has been hours since the procedure and the anaesthesia is long gone, yet I’ve felt barely any pain while literally still having an open wound (no stitches) on my back. I’ve noticed this with other types of pains as well, breaking my wrist, getting bruises from falling and superficial cuts and wounds. The only time I’ve had pain for days was after an actual big surgery. Why is pain often so short lived?
In: Biology
Acute pain is your body telling you to stop whatever it is that you’re doing, **immediately**. Once you’ve stopped and the damage is already done, your body doesn’t need to keep sending that signal.
During acute pain, the nerves in your spinal cord release two neurotransmitters to send the pain signal to the brain: glutamate and substance P. However, if the pain persists, your body may start to produce endorphins. These act to inhibit the release of substance P by binding to opioid receptors. Thus mainly glutamate is released, and your brain perceives this as dull pain rather than sharp acute pain. This is same mechanism as drugs like morphine.
The evolutionary reason is presumably that persistent acute pain can distract you from other important things. So when it seems that there is no immediate end to the pain, the body says “OK, well I’ll dial it down and let you get on with getting on with some basic functions”.
We get pain when a nerve gets stimulated to send a pain signal. If your body is damaged in a way that isn’t stimulating nerve then no pain.
You have three basic types of pain receptors. Mechanical (pressure), heat, and chemical (chemicals released by damaged cells trigger this one).
If you have a clean cut and your body doesn’t inflame the area then there won’t be much damaged cell material floating around to trigger your chemical receptors and without inflammation you won’t trigger the pressure receptors.
So there is little to nothing there for your nerves to detect as painful. Helping this is probably it’s location. Your back has fewer nerves than something more sensorially complex like your fingertips or your eye. A pea sized chunk of flesh cut off of your back won’t compare to an infected hangnail because there will be a tremendous difference in the number of nerves able to send out signals.
Long term pain such as arthritis, never stops causing more damage and triggering those nerves. The swollen joints constantly pressure the mechanical nerves and that same pressure continuously damages cells and triggers the chemical nerves.
Pain originating from the nerves is worse yet. Nerves start reporting pain with no or insufficient stimuli, and since most of our pain reducing medicines treat symptoms or block pain receptors from noticing stimuli, we have drastically fewer tools to combat a nerve that doesn’t care about stimuli and is going to report shit tons of pain regardless.
TL:DR
Pain is not measured in missing chunks of meat is is measured by pressure, heat, and dead cell goop. A clean and uninfected incision or a recovering bone fracture once the swelling has gone down are not experiencing any pressure or heat and the dead cell goop has been cleared away already. Thus no pain.
Pain ( or better, suffering) does not correlate well with damage. Just because something causes pain doesn’t mean it causes damage and just because something causes damage does not mean you need to feel pain.
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