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3.1.3 Olfactory transduction
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From the course by Peking University
Advanced Neurobiology II
51 ratings
From the lesson
Chemosensory system
Meet the Instructors
Chenjian LiProfessor
School of Life Sciences
Donggen LuoResearch Fellow
School of Life Sciences
Yan ZhangProfessor
School of Life Sciences, Peking University
So actually, this feature is quite interesting, right?
So it's [INAUDIBLE] of the cell.
In our brain, in the very early development.
Actually, a similar thing.
The garber effect is depolarized to depolarize the neuron.
Okay, in the early development, some of those neurons actually inside the neurons
may be the correct concentration, it's higher than the extra cellular.
And then in this case, you have a carbon release, and
the cell receives the carbon input, and then depolarized.
But there is a transition during the development later,
and then the garber effect for sure is inhibition okay?
Why you need this kind of amplification?
Our research system.
We talk about a g protein cascade.
There is a good and there is a bad.
The good is, actually, you can amplify the signal.
One single molecule signaling, can be amplified by maybe 20,000 volts, right?
And here, you already, so you [INAUDIBLE] resistant.
We already used that amplification can detect a single photon,
or a single molecule response is large enough already.
Why you need another step to amplify the signal?
>> [INAUDIBLE] >> Okay.
Good. So, you're saying that actually,
the signal actually is produced in this region, then this signal
is propagated to the cell body, to the axiom to fire up transportation here.
There may be this signal, somehow we are partially lost,
and then if you further boost the signal, and then the compensation will happen.
And then to maintain the quality of the propagation, right?
That's a good thought.
Any other sort about this identification
by the channel?
>> [INAUDIBLE]
Limited by long
distance by the air,
so [INAUDIBLE].
>> Okay.
>> [INAUDIBLE] >> Okay,
so you're still, I think, actually, there's
to amplify the signal is because the input is low.
The chemical concentration is quite limited,
because it's a hydrophobic issue.
And then if one could come in, then you have a huge signal.
There's your arguing, right?
But if the signal is already big enough, for example,
the single photon response, already big enough, then actually we don't need,
actually, another empirification,
if that single molecule response can go to the brain
successfully, then why you need actually further boost the signal?
So, olfactory
system is special.
Again, because actually, there is a sensory
neuron directly contacting the environment.
This is a clue to think about if there's an amplification.
Now, the other sense, like our eye.
The photo receptor is so well protected.
[FOREIGN] But the olfactory system directly contacts your environment.
Odor happen.
To then understand conditions, all right?
For example if, for a fish, if you live in the water,
and we talk about actually the olfactory system,
actually this is a transduction region.
Where is this located?
Over a layer of mucous.
And it's the mucous for the animal.
Actually, direct contact with the air, that's fine.
But if for a fish, that mucous actually always contact with the water.
Contact with water, what will happen?
Well, it is destroyed by something, right?
Let's think about it signaling here, okay.
The signaling.
So when you have a channel open, you need what kind of thing?
You need the ion.
[FOREIGN] The channel.
[FOREIGN] What would happen?
No current, no depolarization, if the mucus
actually diluted by the water [FOREIGN] quite a few,
you don't have many [INAUDIBLE] to depolarize into the cell.
That's the trouble, right?
Especially in the fresh water, for example.
The sodium is low.
And the calciums are low.
But actually, in most cases, it's the animal extra cellular solution.
The sodium is about 120 mini molar in that range, okay?
The sodium.
And the potassium would be maybe two mini molar.
And the calcium, it may be one mini molar into the range.
But in the water, those ions quite, quite liter.
So, in that case, even for a fish, if those
sodium ion, you own a little so the ion, or calcium.
So, if you open this channel,
if you have a chemical bind to this receptor, open the channel.
Maybe nothing will happen.
But think about this quiet channel.
If the out of [INAUDIBLE] concentrate is low, actually,
this channel, depolarization would be larger.
It's beneficial if you diluted those concentration outside.
So, the key thing, that is the calcium.
Calcium, what's the difference between the inside of the cell and
outside of the cell, the ratio?
If you learned [SOUND] neuroscience,
these things should be quite clear.
>> [INAUDIBLE] >> Yes, outside is the minimal arrange.
Because of the [FOREIGN].
How about the inside of the cell?
At the resting state,
most of those neurons actually not at that range, it's too high.
It's in the non-normal range,
maybe tens to hundreds of non-normal range in the cell.
When the cell does an excited situation,
maybe they can sometimes go to micromolar range, okay?
Of course, we're talking about the global calcium.
So, in this case, if in the cell
is nanomolar range, and let's make a comparison.
The sodium ion in the cell is about a tenth, maybe a tenth
of a nanomol range, outside the thing is about 100 nanomol range.
So, the inside and outside is about 10-fold or 15-fold.
But for the casing, actually, the inside and outside is huge, right?
It's from mini molar to nano molar.
So, then is about a, what is the ratio?
10 to 26, right?
But actually, as we talk about actually,
it's a tenth of nano molar or hundreds of nano molar.
In that case, maybe ten to four, ten to five, this kind of range, okay?
[FOREIGN] So, if you have those
freshwater diluted at the mucus,
even the calcium maybe was lowered down by a few fold.
Still, inside, outside, is a huge difference, right?
So, when the channel open, calcium, for sure, will go into the cell.
But not much, maybe this sodium in the fresh water.
And then this calcium come in, then we're active here, and.
So, I guess this is already clear.
Why, during the evolution we have this kind of right.
Another step right channel to identify the signal, okay?
>> [FOREIGN] >> Yeah.
>> [FOREIGN]
Fresh water
diluted.
>> [FOREIGN]
>> [FOREIGN]
>> [FOREIGN]
>> [FOREIGN] This
cyclic channel actually not only exists in fish, in amphibians, but also in mammals.
And also in us humans.
[FOREIGN] Later, actually.
So, this channel,
as we discussed, is really important for the fresh water, right?
The animal.
Actually, in the mouth, just actually a few years ago,
one Germany group, delete this channel.
Yes, the [INAUDIBLE] channel,
and then do the behavior study of the mouse.
And then to fault, actually know much, actually,
bad things happen to the mouse, affect the detection, quite normal.
If you, I guess if you take all this in the fish.
In the zipper fish.
Or some frog.
You do the behavior study.
Maybe there was some problems.
As we said, actually, in the land animal, our mucus is actually quite intact, okay?
Contact with the air, that's fine.
Still a lot for iron there, right?
And this already is acute identification steps.
Then you have first one.
According to this study, of course, actually, just one study there, and
then is not so much improvement for the signaling.
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