How does our
sense of smell work?

The full narration of the video.

Pinch your nose, pop a strawberry candy in your mouth, and chew. All you get is sweet, and a little sour. And the strawberry? Gone. Let go, and the strawberry rushes back. That strawberry flavor came from your nose.

Your tongue only knows a few things: sweet, sour, salty, bitter, and savory. Strawberry, coffee, grilled meat: that's all your nose. As you chew, the smell drifts up the back of your throat and into your nose. Pinch your nose, and that path is blocked. So how does your nose know it's strawberry? Let's follow a whiff of it inside.

Everything you smell is tiny molecules floating in the air, far too small to see. Strawberry is a whole crowd of different ones, mixed together. High up, deep inside your nose, is a small patch of moist skin. Millions of smell cells live there. Each cell sends out a few fine hairs. On those hairs are receivers, each one built to catch molecules of certain shapes.

Humans have about four hundred kinds of receivers. The odd part: each cell uses just one kind. Picture an apartment building with four hundred homes, each one expecting only a few kinds of guests. The strawberry molecules drift in and knock on a bunch of doors. Those homes switch on their lights, some bright, some just a little.

When coffee drifts in, a different set of windows lights up. Your brain doesn't check one window. It reads the pattern of lights. Four hundred windows can make more patterns than you could ever count. So four hundred receivers can tell apart far more than four hundred smells. So how does the news reach your brain? Cells with the same receiver all run their wires to the same little cluster.

These clusters sit right above your nose, at the very front of your brain. There, the pattern of lights becomes a map of bright dots. Sight, sound, and touch mostly pass through a relay station first. Smell's main route skips it, and quickly reaches the parts that handle feelings and memory. That may help explain why a smell can bring back a memory in a flash. But the evidence isn't complete yet.

So when you chew that candy, your tongue reports sweet, your nose reports strawberry, and your brain puts the two together into one flavor. Pinch your nose, and far fewer molecules reach the building. The windows stay dark, and the strawberry is just sweet. One more strange thing: these smell cells in your nose are replaced with new ones every month or two.

Most nerve cells in your body can't be replaced. These keep renewing. In your kitchen, which smell takes you straight back to childhood?