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An alarm, not a measurement

Why Does It Hurt?

Pain is not damage arriving at your brain. It is your brain deciding an alarm is worth sounding.

Sensors notice damageA signal runs to thespinal cordThe brain decides whatit meansOnly then does it hurt
Damage is measured. Pain is decided.

  1. Step 1 of 5

    Special endings watch for damage.

    Skin from the side Endings that fire onlyfor harm

    Scattered through your skin and organs are nerve endings that fire only for things that could harm you: crushing, tearing, extreme heat, certain chemicals.

  2. Step 2 of 5

    Two signals leave, at different speeds.

    The fast fibre Sharp, exact, immediateThe slow fibre Dull, vague, a secondbehind

    A fast fibre carries the sharp, precise sting that arrives instantly. A slow one carries the dull, spreading ache that follows a second later.

  3. Step 3 of 5

    The spinal cord acts before your brain hears about it.

    1 Your handtouchessomething hot2 The spine firesthe musclestraight back3 Your brainfinds outafterwards

    Touch something hot and your arm is already moving. The reflex is wired at the spine, and the message reaches your brain after the hand has left.

  4. Step 4 of 5

    The brain decides how loud to make it.

    Frightened and watching itthe alarm isturned upAbsorbed in something elsethe same signal,quieter

    The same signal can be turned up or down. Fear, tiredness and attention amplify it; danger, focus or a good distraction can silence it completely for a while.

  5. Step 5 of 5

    Which is why pain is not a damage meter.

    A paper cut Tiny damage, loud alarmAn injury mid-emergency Real damage, brieflysilent

    A paper cut screams and a serious injury can go unnoticed in an emergency. Pain reports how urgently your brain thinks you should act, not how bad the harm is.

    People born unable to feel pain rarely live long. Without the alarm, ordinary injuries go unnoticed until they are serious.

The short version

Pain is an alarm your brain chooses to sound, not a measurement of damage — which is why the same injury can hurt so differently.

Try it yourself

Bang your elbow and notice two separate sensations: a sharp one immediately, then a duller ache a second later. Two nerve fibres, two speeds.

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