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1.2.1 Review
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From the course by Peking University
Advanced Neurobiology II
58 ratings
From the lesson
Perception: Vision
Meet the Instructors
Chenjian LiProfessor
School of Life Sciences
Donggen LuoResearch Fellow
School of Life Sciences
Yan ZhangProfessor
School of Life Sciences, Peking University
Let's first get an overview of the last lectures.
So we talk about a couple of points.
So first actually for a sensory system
what you need is actually the first step actually is the sensory transduction.
So, what's sensory transduction?
Can somebody?
[FOREIGN] >> [INAUDIBLE]
signal from outside [INAUDIBLE]
>> [INAUDIBLE]
>> Okay.
So sensory transduction is just one step.
The step in converting the physical or
chemical stimuli into electric signal by the sensory neuron, right?
So you talk about, actually, it's a whole process.
Okay, so we also talk about actually when the sensory
cue is transfuced into an electric signal.
Then the electric signal actually exchange information, maybe its action potential.
So, how the action potential codes that sensory information.
We talk about SUD maybe a couple important features of
the sensory stimuli need to be encoded.
So what are important features of the sensory stimuli?
[FOREIGN] So
essentially stimulation you carry some information to the brain right?
What's the important features?
>> [INAUDIBLE] >> The strings, right.
The intensity or the strings, okay.
>> And the [INAUDIBLE] >> What?
Frequency?
>> Okay.
So what we're talking about is the sensory stimuli, sensory cue.
Where the frequency comes from.
>> [FOREIGN] >> Okay,
yeah, is there anybody else that can help?
[INAUDIBLE] Yep.
[INAUDIBLE]
>> Our insipid fear?
>> [INAUDIBLE] part of the spatial [INAUDIBLE].
>> Okay, this is where you are talking about the location or
the receptor field.
Okay so, yes, maybe this are the many other features but there are the three
very important features is the modality is where there is sound or a light.
Okay, there's the first one, the modality.
And then the second one is intensity or the strength.
And the third one, there is timing.
So the timing is very important right?
So whether that stimuli right now happens, or actually happened ten minutes ago.
So these are the three most important features of the sensory stimuli.
And then how the sensory system encodes
this sensory features is what kind of
of code to encode this information?
It's a very Frequency.
>> [INAUDIBLE] >> Okay, so
maybe right use the spike of frequency, right?
So maybe can coat those intensity of strength of the stimuli.
And also maybe the, we talk about actually, the temporal coding.
That it means actually the timing of the first spike firing.
Actually it's very important information.
And also maybe the interval between the different spikes
also carries the information, right?
Of course then it also depends which neuron
gives the firing, and then we'll encode those modalities, right?
Like if you have light coming,
of course the neurons in your eyes will give the action potential firing.
And by then, if you have a touch maybe in the skin, so this neurons
in the weight to the skin will give you the action potential firing, right?
Okay, so we also talked about the receptor field, what's receptor field?
[FOREIGN]
[INAUDIBLE] So we have one example, actually.
Use the skin to illustrate the receptor field concept, all right?
So in the skin, then you have a different neuron.
Those may be with the sensitive receptors
expressing those neurons exterior generate to the skin.
If that neuron generate to that region and you touch here.
That neuron will give you a response or not.
Of course, actually it is far away then they will not give any response.
So then, what's the receptive field?
[INAUDIBLE]
>> Mm-hm, okay, yep.
Any other comments?
>> [INAUDIBLE] >> Yes, okay.
>> [INAUDIBLE] >> Mm-hm.
>> [INAUDIBLE] >> Okay, right,
there maybe quite strict meaning of the receptive field.
It's the danger area, the sensory danger area.
Those areas where you can have direct receipt of the stimulation,
then excites the neuron, right?
We always talk about, actually, so, actually,
it's not specific for the endangered area.
Any area, if you record from one sensory neuron, any area, so you
give it the stimulation, if the neuron can get excited, there's the receptive field.
If at that region also inhibited this neuron, inhibition.
And that's also included in the receptive field.
Okay?
So it's just any mega sensory like a region areas, actually,
give it the stimuli, can change the activity of the [INAUDIBLE] neuron.
Then that region is the receptive field.
The receptive field includes both excitation and
inhibition, this is important, okay?
Yeah, then we talk about, actually, your visual system.
I'll talk about this new circuitry in the retina.
So, we'll talk about how many types of neurons
we mentioned the last time in the retina.
You have photoreceptors, right?
And then you have horizontal cell, bipolar cell.
And then you have cell and cell.
We have five types of neurons, right?
Okay, so for that Neurocircuitry, what's the,
we talk about, actually, the flow of the information.
The vertical flow, then, is from where to where?
Of course, we talk about the [INAUDIBLE] of the neurons, okay?
[INAUDIBLE]
>> Yes, sugar okay to call for the receptor.
>> [INAUDIBLE] >> To.
>> [INAUDIBLE]
>> Okay, so we talked about the visual
are information flow in the retina
from different neurons.
The vertical one is, of course, from top to the bottom, right.
>> To the terminal.
>> To the terminal, okay.
The terminal, then, is the terminal, of course.
Then the information will be sent out.
Then what's the next neuron to receive that information?
Shiao Yu?
Good.
So photoreceptor will transduce the light information and
then converted it into electric signal.
Then will pass this information to the bipolar cell.
And then bipolar cell will transfer this information to ganglion cell.
This is the logical flow of the information.
How about the horizontal information processing?
What did we talk about last time?
[FOREIGN]
>> [INAUDIBLE]
>> Horizontal information, so okay,
we're only talking about in the retina so far, in the eye.
So we have the information flow is vertical one
from photoreceptor to bipolar cell, then to ganglion cell.
And then, that ganglion cell, of course, will send that information to the brain.
This is the vertical flow.
We also talked about,
in the eye, in the retina, there is horizontal information processing.
The lateral one includes
two types of Neuron for the information processing.
Horizontal cell, without axon.
We talk about,
actually, the horizontal cell can connect to different photoreceptors.
And also, the amacrine cell will have two layers.
[INAUDIBLE]
>> Okay, no, let's see.
Yeah, we talk about it here.
Look at this pictures of the vertical floor for
the information is a photo receptor to bipolar cell and then to ganglion cell.
Right, this is the floor of the information.
And also, they have this one, this guy, horizontal cell.
And also, we have this one, endocrine cell.
You see, these two new type of neurons,
they only process information in the lateral direction, okay?
Okay, so we then talk about, actually,
go to the first step of the visual system,
which is the phototransduction.
So we talk about photoreceptor.
So, for a photoreceptor, what kind of structure, like a rod for the receptor.
[FOREIGN] >> [INAUDIBLE]
>> The structure,
the structure of
the cell, [FOREIGN]
Yeah, like a rod shape, right?
[FOREIGN] So include, what kind of regions?
Actually we talked about outer segment over a cell, right?
Inner segment in a cell body, and the axon terminal.
[FOREIGN]
You see, we talk about this structure,
right?
Of a cell, not the photoreceptor.
You have the outer segment here, and
then you have the inner segment cell body, axon terminal.
And where phototransduction happens,
[FOREIGN] [INAUDIBLE] >> Right, only happened at,
so the phototransduction only happened at the outer segment, right?
Okay.
So in the outer segment, that's where phototransduction happens.
So we talk about, initially, the outer segment has a lot of disk.
Those membranes separate from the cell cytosolic membrane.
[FOREIGN] They separate.
So on the disk, then we talk about a lot of proteins.
What kind of protein on the disk membrane
of for the light signaling?
Rhodopsin.
>> Rhodopsin, right, okay.
Rhodopsin then if a photon activates
it will do what kind of thing?
The next step is for >> Information change.
>> Information change.
The 11-cis-retinal to all chains.
Okay, and then the rhodopsin will be activated, right?
What would happen next?
Deprotein, yes.
So then the rhodopsin will activate the G protein and
then the G protein will activate the force [INAUDIBLE] BTE PTE right and
then the PDE will hydrolyze through [FOREIGN] second GMP.
And then wonder what happened?
There's a channel on the cytosolic membrane, there is a CNG channel.
Because typically the channel is opened by the binding of cyclic GMP.
So if you have cyclic GMP drops the concentration and
then the channel will be closed.
And what will happen to the cell?
>> [INAUDIBLE] >> Right.
It's a hypopolarization, that's called light response over the cell,
it's a hypopolarization.
So, this is actually is very different from other sensor remote entities.
Other sensor in most case, if you have a stimulation,
the cell will deal a depolarization called excitation.
Okay, so this is the I guess important
point actually in the last lectures.
[FOREIGN]
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