That's a taste bud.
Contrary to the old textbook diagrams you may recall, it seems each taste bud is capable of registering/transmitting all of the 5 taste sensations. But there are only 5 of those. I thought there were 4, but there's something called "umami" (Wikipedia says it's sometimes called "savory"). It's got something to do with the responding to salts (such as MSG) of glutamic acid, a type of amino acid. Our tongues may or may not be like those of rats with this one (it looks like we don't know), but the brain and synapses and stuff like that there are involved. G-protein-coupled receptors, as with 2 of the other tastes---bitter and sweet---come into play with umami. Then there are also salty and sour.
Anyhoo, discounting what smell may add, all the complicated taste sensations we experience are (still thought to be) made up of just those 5 fundamentals.
If one were to posit that there are just a handful of fundamental emotions that work the same way, what do you think they are? The one that got me to thinking of this notion was the feeling of mourning.