Taste and Smell
So taste and smell often times work together
but these are very separate senses.
In fact, one comes from epithelial source,
and then smell comes from a neuron.
Taste Structure Function Relations.
Here you need to think
about what are taste buds.
Taste buds are going to be these
con clamored of different types of cells.
Different type of cells being type 1, 2 and 3.
All will sense a little bit
different amount of various tastens.
These tastens are going to be
items that will have complexity to them.
And they will also allow you to sense different
parts of the same food in a slightly different way
which cause its unique taste.
So let’s go through how these
different types of taste receptors work.
The first type of taste receptor senses salt.
And this is a fairly straight forward process.
You’ll have sodium in the interstitial fluid or in the
saliva and that sodium will travel through a sodium channel.
In fact it’s an ENaC sodium channel. One that we
talk about in the kidney and other areas of the body.
Sodium travelling through the membrane
causes membrane depolarization.
Has the membrane depolarize?
Calcium is released through
voltage-gated calcium channels.
That particular calcium will then cause vesicles
to dock, and fuse and release a neurotransmitter.
That neurotransmitter is then
sense by a sensory afferent nerve
and will send signal back to
the brain that, that was salty.
How other taste work through
type two receptors?
Bitter, sweet and umami will all be
measured in a very similar manner.
Bitter, sweet or umami.
These are use a gustin G protein.
So as they are transduced this specialized
G protein will stimulate phospholipase C.
Phospholipase C converts PIP to DAG and IP3.
IP3 then travels to the endoplasmic reticulum, binds to
IP3 channels that release calcium into the cytosol.
That calcium is release in
the cytosol will do two things.
One is it activates sodium channels.
And then sodium is allowed
to rush into the cell.
As that happens it also triggers voltage-gated calcium
channels and additional calcium enters into the cell.
This additional mount of calcium that causes vesicles
to dock and fuse and to release sero-neural transmitter
to the sensory afferent nerve.
So doesn’t matter which form of
sweet or bitter that you might sense.
But this will be a complex type of
taste receptor and a complex type of signal
that sent back to the sensory afferent.
Our final type of receptor,
we have is for sour.
Sour, there are couple of mechanisms proposed.
Really, what is sour?
Sour is sensing a hydrogen ion.
So a hydrogen ion can enter the cell
through couple of different manners.
One is with sodium and the other
is it could stimulate sodium.
So how they think this stimulated sodium one works?
Is it works through a TRPP3 channel?
These TRPP3 channel are assets sensing channels
that allowed then sodium to enter into the cell.
Once again, these causes
As you have membrane depolarization,
it activates voltage-gated calcium channels.
Allows calcium influx into this cell,
which then causes membrane docking and fusing
to release a certain quanta of transmitter
substance to stimulate that sensory afferent nerve.
Let’s review these three different cell types again.
For bitter, the substance, which is sense,
has bitter binds to G protein-coupled receptor
increasing IP3 and calcium and opens up a
special TRP channel which depolarizes the cell.
Sweet, umami working in a
similar manner to the same mechanism.
These both are considered type 2 cells.
Sour is a type 3 cell.
In these senses, hydrogen ions.
And these stimulates hydrogen ions to allow sodium
to enter through asset sensing TRPP3 channels.
This again causes depolarization of the cell.
And therefore, sending its transduction
of taste back to the brain.
And then, finally we have salt.
And salt enters by these ENaC sodium channels, depolarizing
the cell and causing that signal to be sent back.
So doesn’t matter which of these four
different classifications that you use,
any particular food will sense them almost all.
You will have a different conglomeration of
activating on these different four receptors
throughout the whole mouth.
As they are sensed that taste will be a complex
mixture of something that will stimulate sweet,
maybe a little sour, maybe a little salty
and at different portions of the tongue.
How do you integrate these large taste responses?
Well, we have three main cranial nerves that
will send the information back to the brain.
We have the facial nerve,
the glossopharyngeal, and the vagus.
All these will coordinate the information
that’s being sent back to the brain.
The other pieces of taste that are part of the
traditional taste receptors are such as fill of the mouth.
You may have a substance that feels crunchy
or maybe that substance feels soft or gushy.
All those mechanical receptor information, they are
sent through a little with different mechanism.
That is just like the same kind of mechanical
information that’s sent through the skin.
You can also sense items
that are hot or burning.
And this is a temperature, this is a molecule
such as capsaicin sensing they particular receptor.
So that is outside of taste but yet
its integrated at the same time.
So its always a very complex feel, for when
you get something in your mouth to determine
how it taste to you.
And you all know that different
people have different taste.
Some people have very spicy taste.
Other people have very blunt taste.
And its just part of how that information of
the food stuff that we’re entering into our mouth
gets transmitted back to the brain.