Eli5 why rubbing my shin after a blunt force trauma (I kicked against the table) reduces the pain sensation significantly?

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Eli5 why rubbing my shin after a blunt force trauma (I kicked against the table) reduces the pain sensation significantly?

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Think of nerve pathways like a water hose and hot water equals pain. When you hit your shin the only message being sent down the neural pathway/water hose is very hot water. By rubbing your shin, you are adding another sensation to the neural pathway similar to turning on the cold water to the water hose. The pain sensation is diluted just as the cold water cools the hot water traveling through the water hose.

TENS units work similarly. You place them where you are in pain and the electrical impulses “dilute” the pain

There are two nerve pathways going from your skin to the spinal cord: touch and pain. From the spinal cord, they go up to the brain where they activate emotion and fear centres etc. At the spinal cord, the touch pathways inhibits the pain pathway and according to the Gate Theory of Pain, rubbing the hurt area causes the touch pathway to inhibit the pain pathway at the spinal cord so it does not go up to the brain and that is why there is some analgesia when you touch the hurt area. After a while though, the pain pathway from the hurt area becomes sensitized and touch becomes a pain signal (i.e. inflamed skin).

Pain is sensitive to distraction or dilution. Basically you add more sensory input from the same area of the body, and the brain notices the pain less, mixed in with the additional sensations. It’s the same principle with rubbing various lotions on painful areas. They cause the skin near the injury to feel uncomfortable – prickly or hot or cold – plus usually a medication-like odor such as menthol, that further confuses your brain, causing a placebo effect, and the original pain is somewhat blunted by all this extra information.

Holy shit a question that is specifically applicable to me! I’m a pain management physician.

So someone below said the “gate control theory of pain” which is basically correct when broken down into laymens terms.

To go into a little bit more detail, there are several different types of sensory nerves. There are nerves that sense pain, but also vibration, temperature, touch, etc…

Nerves that sense PAIN causes spinal cord receptors to “open” their gates allowing tons of information to go up the spinal cord to the brain.

In contrast, Nerves that sense VIBRATION, TEMPERATURE, TOUCH, etc…typically “close” these gates and INHIBIT information from traveling up the spinal cord to the brain.

This is why after hitting your shin, nerves that sense pain are firing to the spinal cord, and then when you rub your shin, nerves that sense touch and vibration, are trying to inhibit the nerves that sense pain from firing to the spinal cord.

Even weirder, phantom pain in your arms, wrists legs and feet, caused by inflammation of the nerves leaving your spine, also feels better when you rub it even though there was no damage to the area you’re rubbing. When I asked my physical therapist why it felt better to rub it even though there was no physical damage, they said “everything feels better when you rub it!”