- In this video, I want you to think about taste
in a completely different way
to how you normally do.
These five tastes that we sense with our tongues
are actually five different
chemical detection mechanisms that help us to survive.
Take sweetness, for example,
that's our sugar detecting mechanism.
Or to put it in survival terms,
it's our energy molecule detection mechanism.
Sugar molecules are full of energy
that we can easily access.
So it makes sense from an evolutionary point of view
to be able to detect these molecules
when we put them in our mouths.
It's really important for the correct functioning
of the chemistry that goes on inside our cells
to have the right level of salt in there.
So it makes sense from a survival point of view
that we can detect salt that we're putting in our mouth
hence our ability to taste salt.
What about savoriness, sometimes called umami?
It's called umami because Japanese scientists
were looking at this stuff way before anyone else
and umami is their word for it.
It roughly translates to deliciousness.
Well, umami is our protein detecting mechanism.
Humans need protein in their diet.
Actually we're not detecting proteins directly
with that taste,
we're actually detecting molecules called glutamates,
and you tend to find glutamates
in foods that are high in protein.
So it's a proxy mechanism.
Do you know what, it's such a strange taste to experience
in pure form 'cause glutamate is used as an additive
a lot in Chinese cuisine.
At least in the UK it is.
So to my palette, it tastes like some essence
of Chinese food.
Like some element of Chinese cuisine
has been distilled into crystal form.
By the way, if you like MSG, don't worry about it.
The MSG scare was not founded on scientific research.
It was founded on speculation.
And subsequently there has been no good evidence
to link the consumption of monosodium glutamate
with all these side effects like headaches and stuff.
Sour taste is our acid detecting mechanisms.
Scientists aren't completely sure why we have it
but some believe it helps us to figure out
whether fruit is ripe or not.
And finally, bitterness is our poison detecting mechanism.
That all makes sense, but it gets weird.
Like there are taste receptors in our guts, for example,
what the hell are they doing there?
Wait, what the fu...
And there are plants that can trick our sense of taste
and make us do things for the plant.
And we get nothing in return.
I'll get to all that eventually
but first I wanna talk about how these different
chemical detection mechanisms work
because they're really clever.
Let's look at sweetness first.
On your tongue there are these lumps called papilla
and each papilla contains several taste buds,
and each taste bud contains several taste cells
or gustatory cells.
And look at the top of those cells
where the cell comes into contact with your saliva,
there're all these little hairs.
Let's zoom in on one of those hairs.
We're looking at a cross section
through the cell membrane that phospholipid bilayer.
And look here's a molecule that straddles the bilayer.
There's a bit on the outside and a bit on the inside.
And you'll notice that the outside
has a very specific shape.
It's the old lock and key analogy.
When a molecule comes along, that's just the right shape,
it fits into that protein
and a confirmational change happens.
The shape of the protein changes
and that causes a change on the inside as well.
And that leads to some chemical reaction
which ultimately leads to a signal being sent
down nerves to the brain
and you register that as something sweet.
Umami works in the same way
except that instead of detecting sugar molecules
it detects glutamate molecules.
Bitterness works in the same way as sweetness and umami,
but it is different.
With sweetness you're detecting sugar molecules,
with umami you're detecting glutamates,
but with bitterness you're detecting
a whole range of chemicals.
So instead of this one receptor
that detects specifically sugar
or one receptor that detects specifically glutamates,
humans actually have 25 different bitterness receptors.
Because, of course, there are all these poisons out there.
This variety of receptor molecules is driven
by the evolution of plants.
Plants that don't want to be eaten.
They're coming up with novel poisons all the time
and so we have to evolve to keep up with that.
So it's not that certain chemicals happen
to taste bitter,
it's that our bodies have evolved this aversion response
to molecules that harm us.
Your salt detecting mechanism works differently
to sweet, umami, and bitter.
It still happens on the gustatory cells
with those little hairs,
but instead of it being this lock and key
type receptor proteins that straddle the membrane
of the cell,
and the sugar molecules can attach to.
Instead you get these tube-shaped proteins
that create essentially a hole into the cell
through which certain things can pass.
In this case, sodium ions.
When salt dissolves in your saliva,
the sodium and the chlorine separate.
The sodium ends up with a positive charge
and the chlorine ends up with a negative charge.
And it's these positively charged
sodium ions that can pass through these tube shaped proteins
in the membrane of the gustatory cells.
The special tube-shaped protein
called a sodium channel
allows sodium ions into the cell and nothing else.
And as the sodium ion concentration increases in the cell,
that leads to a cascade of chemical reactions
that ultimately leads to a signal
passing down the nerves to your brain,
and you experienced that as saltiness.
Your acidity detecting mechanism,
in other words, your sour taste receptors
work in a similar way.
Something is acidic if it has a high concentration
of hydrogen ions.
So the gustatory cells in charge of your ability
to detect sour things must be able to detect hydrogen ions.
And again, it's a tube-shaped protein
that allows ions into the cell
but this time it allows hydrogen ions, not sodium ions.
And once again, that increase in concentration
in hydrogen ions, inside the cell leads
to a signal passing to your brain
that you experience as sourness.
But wait a second, what is a positive hydrogen ion?
You might know that a positive ion is an atom
where an electron has been stripped away
leaving it with a positive charge.
What does that look like for hydrogen?
Well, the nucleus of hydrogen is just a proton.
It's the simplest of all the atoms
and it has a single electron and an orbital around it.
So to make it into an ion,
you strip away that electron,
then, of course, all you're left with is a proton.
A hydrogen ion is just a proton.
So when you taste something sour
you're tasting protons.
Protons tastes sour.
Isn't that wild?
Who would have thought a subatomic particle
could have a taste?
This lock and key mechanism used by sweetness,
savoriness, and bitterness.
Actually your body uses that mechanism all over the place.
For example, with hormones, like if you get a spike
of adrenaline, those adrenaline molecules
attach to receptors on the outside of your cells
changing the way those cells behave
in preparation for a fight,
or in preparation for you to run away.
The same mechanism is used by your sense of smell.
You have all these receptors in your nasal cavity as well.
All this raises a philosophical question for me
which is why I've sat down.
It's just a bit more,
like how many senses do we have?
There's the traditional five senses from Aristotle
that are still taught in schools today
despite the fact that no scientist thinks
that we have five senses.
Like obviously, we have way more than that.
In addition to touch, taste, smell, sight, and hearing,
we can also sense the temperature of our environment.
Thermoception we know when something is hot
and that's clearly distinct from our sense of touch.
We can also sense the orientation
of Earth's gravitational field.
Otherwise we'd fall over all the time.
That's our sense of balance or equilibrioception.
That's managed by our inner ear
but it's clearly distinct from our sense of hearing.
In addition to that, some people say we have
a sense of thirst and a sense of hunger
and there are a few more like that
but I wouldn't want to call those senses
because they're not telling us
about our external environment.
They're telling us about ourselves,
and semantically that doesn't seem
like a good definition for a sense for me.
But anyway, the point I wanted to make
was maybe we should be splitting up
the five tastes that we sense on our tongues
into five different senses
because they detect five different things,
they elicit five different responses,
and they serve five different purposes.
These five tastes are all examples of chemoreception,
our ability to sense the chemicals in our environment.
And we've chosen to group them together.
So maybe we should group together all our chemoreception,
but then actually our number of senses goes down
by one because we're lumping in our sense of smell
with our sense of taste.
It's all chemoreception.
But maybe it makes sense to split them up
because they're on different organs.
You've got the nasal cavity
and that's separate from the tongue.
You could also say,
well, taste is about molecules dissolved in saliva
and smell is about molecules in the air.
Okay, but what about molecules in the stomach?
Because remember we have taste receptors in our guts,
our airways and our urinary tracts,
are they three separate senses
because they're three separate organs as well?
Or maybe they're not senses at all
because we're not consciously aware of their function.
And maybe that's part of the definition of a sense.
So the answer to the question,
how many senses do we have is: it depends.
And that's interesting in itself.
I wanted to talk about what the taste receptors
in your gut are doing,
'cause it's really interesting.
Also the evolution of taste is really interesting.
And I promised I'd talk about this plant
that tricks us into helping it.
Actually it tricks gorillas, not humans.
But anyway all that stuff together is quite a neat package.
So I'm gonna make a separate video about all that stuff.
If you're interested, make sure you've subscribed
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