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2.2.5 Sound transduction-V
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来自 Peking University 的课程
Advanced Neurobiology II
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Perception: Auditory
与讲师见面
Chenjian LiProfessor
School of Life Sciences
Donggen LuoResearch Fellow
School of Life Sciences
Yan ZhangProfessor
School of Life Sciences, Peking University
This protein called prestin and they are multi sensitive.
They are not I only our own channel.
[FOREIGN].
These proteins are sensitive to the voltage and
at the same time the voltage can drive the protein,
actually wether elongate or just the short one.
Okay, it's quite unique.
Now the situation is actually when the cell is hyperpolarized
this protein actually is in the long state.
Okay?
[FOREIGN].
But when the cell is depolarized,
those proteins actually get very short.
So imagine, okay, there is a force coming, mechanical force.
Moves the hair bundle, okay, moves the hair bundle in this direction.
And the mechanical sensitive ion channel will open.
And the potassium ion will go into the cell and the cell reacts.
And then because this protein is sensitive to the voltage,
then this protein will get shorter and the whole cell actually will get shorter.
This is the first phenomenon for this cell is actually
the soma can change the lens,
responding to a sound simulation.
At the same time this hill bundle also can
have some movement when you have a force coming.
And the cell, they polarize calcium.
The potassium ions, and the calcium ions will go into the cell.
The calcium will move.
Actually, it's [FOREIGN] further away from the stimulation, like this.
This is also another step for the amplify.
The sound stimulation.
Okay, take a look.
There are two steps.
Y is actually the hair bundle if you have a mechanical A stimulation.
And then the mechanical sensitive ion channel will open, and
then the calcium will go into the cell and make the bundle further move.
[FOREIGN] The second thing is actually
the sound coming to move the hair bundle and
then of course is the basal membrane
will make the movement and then the cell will depolarize.
And this will make the cell depolarization, right.
Depolarization will make the cell became shorter.
Because this protein.
And make shorter and then [INAUDIBLE] Basic
membrane will further displace and then.
You that sound information.
And stimulation in the.
And there are two steps for
the of this cell signal, okay?
Is it true?
How can you demonstrate this properties of the cell?
>> [INAUDIBLE] >> Good.
>> [INAUDIBLE] >> Good.
So If you look at this protein and
the inner health cell, the sensitivity will be decreased right?
Okay tasted good but does not actually directly demonstrate.
That change of these cell lens, right?
It's just actually the down stream effect.
How can you directly demonstrate that point about the cell mortality?
Okay, good.
So if you isolate distant cell and then you give the mechanical stimulation.
Then just by looking at it under the microscope,
see [INAUDIBLE] the cell can really change the [INAUDIBLE].
If you see the change, of course, then is a direct demonstration.
I guess I should give another lecture for the physiology class.
So, indeed, people did the experiments.
They isolated a hair cell.
Of course, this one, this is an outer hair cell.
And, then you can see actually this is
we have a [INAUDIBLE] here, okay?
Doing the [INAUDIBLE].
And then this region actually it's the [FOREIGN].
In this case we just want to demonstrate is the cell depolarized or
hyper polarize strength which changes the length okay.
So it's quite easy to achieve with this manipulation
that is the biggest way we can do the sample with the cell.
Then we can inject the current, into the cell make it depolarized.
Or we inject sound as a current current.
Then the cell will hyperpolarized.
Okay?
So here actually at demonstration was the,
then inject the sound current.
You cannot see it, listen to it.
But you can see the injection of the current.
Actually you follow that music the rock music.
You can see here.
[MUSIC]
So I guess this already very convincing actually,
is really direct, is that the cell can move.
So then you can think okay, in the natal condition,
then you can because of this cell, see it here right?
This is the base cellular membrane and then this is another membrane.
Now, but
the main is because the sound coming is actually wipe away to this membrane.
We talked about actually the frequency of this distribution, right?
And then right now if we have our stimulation coming in the cell get shorter
and then this will first move.
As the hair cell we receive a larger sound stimulation, right?
So okay, this is a cartoon to show this is a normal condition.
For example, if you give a sound stimulation to this
structure of the cochlear.
Then, this is maybe, for example,
a high frequency stimulation.
And then this basilar
membrane will make this movement okay.
This is under normal conditions that's included two signal cells.
Why is real sound coming outside?
The second is the inner hair cell contribution.
So if you kind of,
if you disrupt this outer hair cell
of course then, you limit the hair cell contribution, that's what happening here.
The response, they're in the, this tract treatment under their
hair cell cannot transfuse the light signal, to electric signal.
And then you have very tiny movement of the basilar membrane.
This is actually a mechanical movement by the sound of surf.
Okay?
So it is quite obvious obviously then the other hair cell can contribute for the.
This summary about this part.
So mainly we talk about the transduction from the hound cell is a direct
mechanical gating of the own channel, and the compare is
the G mediated protein signaling, for example, into further receptors.
Then this is the key difference between these two signaling.
In the G protein signaling you have a huge amplification.
But then the speed is quite slow, okay.
For this then you have
low amplification by the transduction itself cascade.
Okay?
But you have a very fast response.
At the same time, in the auditory system, in order to make it sensitive
to the sound, then you have another type of cell called outer hair cell.
To have with the pressed in expression, and
then you can further amplify the mechanical force.
So we talk about, actually, after this
mechanical force, coding by the electric signal in the hair cell.
Next step of course then, is how this signal actually go to the brain.
Right?
So, in the visual system how does the visual information
flow from the photoreceptor to the visual cortex?
[FOREIGN]
So from the photo receptor.
First actually, coming down to the bipolar cell right?
>> Okay and then?
[INAUDIBLE] >> Yes, to ganglion cell.
And then?
>> [INAUDIBLE] >> To LGN, yes, and visual cortex.
Good, thanks.
So that's actually the light signal.
First they produce by the photo receptor and
then go to the bipolar ganglia cell to LGN then to a racial context.
During each steps actually the signal is not passively transported.
There is a lot of connotation.
You talk about actually there is a receptive field.
From the center surround
to the the light bar and also maybe to free cell.
Right?
Of course and then for this system, again signal strategy again what happened.
