Pain, the Gate Control & Why Rubbing Helps
Bang your elbow and your hand flies to rub it — before you even think. That reflex is real physiology. Pain signals from the skin have to pass through a gate in your spinal cord before they can reach the brain, and rubbing the spot fires touch fibres that help slam that gate shut. Press play to watch pain spikes race up the nerves to the cord, then rub the skin and see them pile up at a closing gate instead of reaching the cortex — the reason a squeeze, a cold pack, or a TENS machine can genuinely dull pain.
Try this: start on Painful stimulus and watch the pain climb to the brain, then hit Rub the skin and see the gate close and the pain number fall. Then try Chronic wind-up to see how the gate can jam open.
Live pain readout
What's happening
The conduction speeds (Aδ ~5–30 m/s, C ~0.5–2 m/s) and the 0–10 numeric pain scale are real clinical values. The gate’s percentage “openness” is an illustrative model — Melzack & Wall’s gate is a concept for how these circuits interact, not a single measured valve.
The Science in Plain Language
1. Pain starts as a warning signal, not a wound
The very first thing to understand is that pain is not the same as damage. What the skin actually detects is a threat — too hot, too sharp, too much pressure, the wrong chemicals. This job is done by nociceptors: free nerve endings that thread through your skin like the exposed tips of tiny wires. When they are pushed hard enough, they fire electrical spikes toward the spinal cord. Those spikes are only a message. Whether you actually feel pain — and how much — is decided further up the line, in the cord and the brain.
2. Two fibres, two kinds of pain
Stub your toe and notice you feel it twice. First a sharp, bright, exactly-located jab; a beat later, a duller wave of burning ache. That is two different nerve fibres arriving at two different speeds. The sharp “first pain” travels on Aδ fibres — thin fibres wrapped in fatty myelin insulation that lets them conduct at roughly 5–30 metres per second. The dull, burning “second pain” travels on C fibres, which have no myelin and creep along at only about 0.5–2 metres per second — slow enough that the ache noticeably lags the jab. Both are real, both are useful, and you can watch the fast red spikes outrun the slow orange ones in the animation.
3. The dorsal horn: where the message is judged
The fibres dive into the back of the spinal cord and end in a region called the dorsal horn — the upper wings of the butterfly-shaped grey matter you see in the diagram. There they hand their signal, using neurotransmitters like glutamate and substance P, to a projection neuron (older texts call it the transmission or “T” cell). Its long axon crosses over and climbs the spinothalamic tract up to the thalamus and then the cortex. Only when the cortex lights up do you consciously feel pain. This is why pain is genuinely made in the brain, not in the skin — the skin only sends the raw data.
4. The gate — and why rubbing helps
In 1965 Ronald Melzack and Patrick Wall published the gate control theory in Science, and it changed pain medicine. Their insight: sitting between the incoming pain fibres and the projection neuron is an inhibitory interneuron that can turn the volume down — a gate. Large-diameter Aβ fibres, the ones that carry ordinary touch and vibration, excite that inhibitory interneuron. So when you rub, press, or shake a banged elbow, you flood the dorsal horn with Aβ touch traffic, the interneuron fires, and the gate swings partly shut — fewer pain spikes get through to the brain. Hit Rub the skin and watch the pain spikes literally pile up at the closing gate. This is not folk wisdom; it is the same principle behind a TENS machine, which buzzes Aβ fibres on purpose.
5. The brain fights back: descending control
The gate can also be closed from above. From the periaqueductal grey in the midbrain, through the rostral ventromedial medulla, the brain runs pathways down the spinal cord that release serotonin and noradrenaline and trigger the cord’s own opioid chemicals — endorphins and enkephalins. These press the gate shut. It is why a soldier can run on a broken leg, why fear or focus can blank out an injury (stress-induced analgesia), and a big part of why a placebo can genuinely relieve pain — placebo relief can be partly reversed by naloxone, the same drug that blocks opioids, which tells us the brain’s own endorphins are doing real work. This descending system is also the target of antidepressant-class drugs like duloxetine, which lift serotonin and noradrenaline to strengthen the brakes.
6. When the gate jams open: wind-up and chronic pain
Repeated or intense C-fibre firing can make the dorsal horn neurons progressively more excitable — a process called wind-up, driven largely by NMDA receptors. Keep it up and the cord undergoes central sensitisation: the gain is turned up so high that the gate effectively jams open. Now a light touch is read as pain (allodynia) and real pain is amplified (hyperalgesia). Press Chronic wind-up to see even gentle input reach the cortex as strong pain. This is the engine of much chronic pain, and it explains a hard truth: in a sensitised nervous system, hurt does not reliably mean harm. The alarm can keep ringing long after the tissue has healed. (The drug ketamine blocks NMDA receptors, which is one reason it can quiet this kind of pain.)
7. What the medicines actually do
Each major pain drug works at a different point in this circuit. NSAIDs (ibuprofen, naproxen, aspirin) block the enzymes COX-1 and COX-2, cutting production of prostaglandins — the chemicals that sensitise nociceptors in inflamed tissue. That is peripheral: fewer, weaker spikes leave the skin in the first place (toggle NSAID to see the traffic thin out). Opioids (morphine, codeine, oxycodone) act centrally on mu-opioid receptors, pressing the same endorphin gate the brain uses — powerful, but with tolerance, constipation, and overdose risk. Gabapentin and pregabalin bind the α2δ subunit of voltage-gated calcium channels to quieten over-firing fibres in nerve pain. Local anaesthetics like lidocaine block sodium channels so the wire cannot fire at all, and capsaicin (from chilli) first excites and then exhausts the heat-sensing TRPV1 endings. Different door, same house.
8. The honest myth-correction
The tidy picture — a stubbed toe sends “pain” up a wire and the brain reads it off — is wrong, and believing it makes pain worse. Nerves send only threat signals; the brain constructs the experience of pain, weighing context, mood, attention, past injury, and fear. That is not “it’s all in your head” — the pain is completely real — it means the volume knob is genuinely adjustable. Rubbing, heat, cold, movement, calm breathing, sleep, and understanding the mechanism are not tricks; they nudge real gates and real descending pathways. And the gate itself is a model, not a literal measured valve: it captures how touch, mood, and the brain’s own chemistry shape pain, and it has held up remarkably well since 1965 — but the percentages on this page are there to build intuition, not to report a lab number.
9. What you can actually do with this
Practically: for a fresh bump, rub or apply firm pressure — you are firing Aβ fibres to close the gate. Heat or cold, gentle movement, and TENS all work partly through the same touch-gate route. Slow breathing, focus, music, and reassurance recruit the descending brakes. For persistent pain, the goal shifts from “kill the signal” to “calm the sensitised system” — graded activity, sleep, and sometimes nerve-targeted medicines rather than escalating opioids. See a clinician promptly for pain that is severe, spreading, comes with weakness, numbness, fever, or follows a serious injury — that is your alarm doing exactly the job it evolved for.