How your body turns heat and a touch into a nerve signal

Close your eyes and someone hands you a warm mug. You feel the heat. Press a finger on the table and you feel the push. But how does your skin actually turn 'hot' or 'a touch' into something your brain can read?

The answer is tiny gates called ion channels, sitting in the endings of your nerves. A gate stays shut until the right signal arrives. When it opens, charged particles rush through, and that little jolt makes the nerve fire off a message to your brain.

So the burn of a chili and the warmth of a mug pull the same trick on your body: both open the heat gate. And a poke, a hug, or the floor under your feet all open the touch gate. Same idea, two different doors.

Your sense of temperature and touch is called somatosensation. For decades scientists knew the skin could report heat, cold, and pressure, but not which molecules did the reporting. The 2021 prize went to the people who found them.

David Julius started with a clever probe: capsaicin, the compound that makes chili peppers feel hot. He built a library of genes switched on in sensory neurons and dropped them, one batch at a time, into cultured cells that normally ignore capsaicin. After a long search, a single gene made those cells respond. It coded for a brand-new ion channel, later named TRPV1.

The same trick uncovered cold. Working separately, Julius and Patapoutian both used menthol, the cooling compound in mint, to find TRPM8, a related channel switched on by cold.

Touch was harder, because the trigger is a physical push, not a chemical. Patapoutian's team found a line of cells that gave off a tiny electrical blip when poked with a micropipette. They lined up 72 candidate genes and switched them off one at a time. When one particular gene was silenced, the poking went unfelt. They had found a mechanically gated channel and named it Piezo1, from the Greek word for pressure; a close relative turned out to be Piezo2.

TRPV1 is a nonselective cation channel and the prototype of a polymodal sensor: it funnels several painful inputs onto one pore. Heat above roughly 43 °C, protons from acidic tissue, capsaicin, and certain endogenous lipids all converge to open it. Capsaicin binds a pocket in the channel's transmembrane region, and the open channel passes Na+ and, importantly, Ca2+. The resulting depolarisation of the free nerve ending drives action potentials along nociceptive fibres toward the spinal cord.

The methodological lesson is expression cloning with a functional readout. Julius did not purify a protein; he used capsaicin sensitivity as a selectable phenotype and let the cells report which cDNA conferred it. That logic generalised by swapping the probe: menthol revealed the cold channel TRPM8, and a mechanical poke revealed Piezo. The pattern is reusable: pick a stimulus you can apply at the bench, build a cellular readout that answers it, and the responsible gene falls out. Decades of physiology had described these sensations in detail without a single molecule attached to them, so the prize rewards turning each feeling into a named, testable protein with a known pore and a known trigger.