Science Questions

Is spicy a taste?

Tue, 23rd Feb 2016

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Android Neox asked:

Why is hot, as in spicy, not a taste? Because there are no taste buds for it?


Kat put this zinger to Chris...Chilli peppers

Chris -  Well actually, someone wrote on the Naked Scientist web forum, which you can go to:  They said -  rub some chilli in your eye and then youíll understand itís not about taste - itís about pain.  And the answer to this question is, actually, an anatomical one and a functional one.  We tend to talk about five different tastes or taste sensations: bitter, sweet, salty, and sour.  And they are recorded or detected on your tongue by what we call taste buds, which are specialised clusters of nerve endings which are covered in receptors - these are molecules that can lock onto various things in food and they then signal to the nerve and tell the nerve to fire off impulses to your brain stem, which then tells your brain "this is what I am tasting."  And thatís confined to the tongue and there are two nerves that do that job; thereís a nerve at the anterior (the front) two thirds of the tongue called the chorda tympani, which supplies some of those taste sensations; thereís another nerve called the glossopharyngeal nerve, which innervates the back third of the tongue.

Now pain, on the other hand, is not just restricted just to the tongue. You can sense those sensations all around your mouth cavity, all over your tongue, and in your throat.  And chilli is capsaicin (thatís the molecule), and it binds onto a totally different class of nerve fibres called C-fibres.  They have on their surfaces a certain molecular docking station or receptor called TRPV1. When the capsaicin binds onto them it triggers a burning - or heat - sensation; those same nerve fibres also tell you whether something is hot or cold. So, in other words, what we call taste is detected in a very special way in a very special place by a very special cluster of nerves.  Those pain sensations are detected alongside all the other sensations you can feel in your mouth by the trigeminal nerve, so itís anatomically different and itís functionally different.  Therefore we donít regard the chilli pepper taste as a taste, we regard it as a sensation.

Kat - And presumably this is why the saying goes - a really really hot curry or a chilli ďwill burn on the way out as well as the way inĒ.

Chris - It does.  You donít have very many of those pain fibres innervating the rest of your GI tract. But your mouth and your bottom end, those actually are made by the outer layer of your body embryologically, the outer coating of your developing embryo, growing in and uniting with your gut tube and taking with it the kinds of nerves that are there.  And your trigeminal nerve is the nerve concerned, and thatís the one thatís got the receptors for chilli. Which is why, yes, youíre very sensitive on the way in, and very sensitive on the way out, if itís a hot one...


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Hi Michael

spiciness is not detected by your taste buds in the same way that salty, bitter or sweet flavours are. These latter taste stimuli are detected by specific classes of nerve fibres carried in two anatomically discrete nerve bundles that terminate in the taste buds. The front two thirds of the tongue is supplied by the chorda tympani nerve and the posterior (back) third of the tongue is supplied by the glossopharyngeal nerve. The taste sensations carried by these nerves are transmitted to a region of the brainstem called the nucleus tractus solitarius, which relays them upwards into the brain.

But if one looks at the nerves that are sensitive to spicy sensations, which are small calibre (C and A delta, to give them their proper terminology) fibres that express receptors for capsaicin (the pungent chilli chemical), these nerves are part of the trigeminal nerve and are found throughout the oral cavity, rather than forming interactions with taste buds. Tracing them into the brain, they connect to a different site called the sensory trigeminal nucleus.

So, in summary, the chilli-sensitive nerves are differently distributed around the mouth and connect to a different target in the brain compared with classical taste nerves; therefore they - and the sensation the subserve, which is detection of heat and cold - are not considered a taste. chris, Fri, 19th Feb 2016

If you get chilli powder in your eyes you will realise that it doesn't just affect sensors that respond to taste. Bored chemist, Sat, 20th Feb 2016

Good call!

...but not just eyes either! I had a colleague working on capsaicin in the lab. His gloves leaked, as he discovered when he went for a wee, mid-experiment... that certainly did bring tears to his eyes, despite being at the other end of the body... I am also aware of at least one amorous couple who did a similar experiment on each other after earlier cooking curry that involved chopping fresh chillies. chris, Sat, 20th Feb 2016

It's an old joke that you can recognise chemists because we are the people who wash our hands before going to the  bathroom.
I gather chefs in Mexican restaurants may be mistaken for chemists. Bored chemist, Sat, 20th Feb 2016

Funny, herpes virologists have that reputation too... chris, Tue, 23rd Feb 2016

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