Who is this gentleman? [FOREIGN] Okay. This is Alan Hodgkin. If you study neuroscience, I guess you should be able to recognize these pictures. Alan Hodgkin the father of the neuroscience. I guess actually nobody will argue. Because actually he made great contributions to understand the action potential, right? How those, [INAUDIBLE] Sodium channel and the potassium channel to shape the, generate the action potential. And of course, the H there are the model the function actually is so famous actually. So, but it's actually quite interesting. After he finished the classical work on the action potential and then he switched the research field. That's a switch to this research system. So, third time he actually he tried to identify a new research field that is actually has very important questions here, but actually is solvable that's important. So then he tried to understand how the photo receptor actually convert the light signal into the electric signal. There's actually studies of photo transduction. And then, he trained quite a few people, here, in the photo transduction field. Let's look at this four gentlemen. This one is Dennis Baylor and this is King-Wai Yau. Dennis Baylor from Stanford. King-Wai Yau from Jones Hawkinson Medical school. And Trevor Lamb from Cambridge University. And also Lamb. So, these four actually are all associates with Alan Hodgkin. And they play a key role in the photo transduction field. This one and this one is the Academy of Mission Science USA. And this one is also one in UK. [FOREIGN] Okay? [FOREIGN] These four, this one actually died quite early. But at these three and this one and this one is still active in the research, and I was a poster of King Wai Yau. And okay so, essentially actually all those kind of photo transduction, the electrical signalling study kind of related to these groups. Of course there are some other researchers actually, don't have any connection with Allen Hodgkin but actually his kind of methodology, the thinking of the research actually influence is a whole field. Let's take a look here. So, look at here, then the Baylor and the Yau and the Lamb are all just three are Allen Hodgekin is a student, a post doc. And they developed a method called the Suction Pipette Recording you see this suction pipe recording. This actually just after a few years, the the development of that methodology and then they kind of more with the idea of suction-pipette recording. So as we said, the sales of the photo receptor has a kind of long out segment here. This is a piece of the retina from a frog okay from a toad. You are in the regional sales. And then you have a pipette here, that pipette you can choose to open it. This is a glass pipette 40 inch, you can choose to open it here. This opening should be smaller than this one. Okay, then you use this opening to suck this cell into the opening. Of course the inside you had is the solution for the electrical combatant. And then, the cell, the membrane, we'll have a contact with this pipette, the wall. For [FOREIGN] and then you see this. Then you can recall the electrical signal. The outer segment actually on the membrane you have this c and g channel. You have a light coming, that channel will close and the cell will hypopoloroid and then you will recall this signal. And the reason is it very cool then you can differ the light to stimulate the cell. You see easily use this vertical one or horizontal one. Or use a full field like stimulation or use different columns, or use different intensities. Okay, then you can do the recording. Here is the recording they got. Look at it here. This is the electrical, current okay. This is the time. This is the light stimulation, quite short just a pulse of the light. And then this is the response at higher and higher light intensity. And the eventually actually saturated there. The response will not grow bigger, but actually just get longer if we increase the intensity. The response lasts longer. This is kind of typical. Maybe essentially for any neurons we have this kind of behavior. You have a threshold, a threshold in the cell giving the response. And then, essentially in the cell will be saturated because of the channel. The maximum channel on the membrane then you'll feel open to those channels and they all close, then the cell will not give anymore response. So, look at this one. Immediately you will trigger your thinking. The thinking is that this is actually relative light. Happens. Happen at this region. So what it tells you? But actually look here. All these response actually start from the end of the stimulation and then the maximum response actually happens maybe 1.5 second later. That's quite strange right and they base it on this kind of thing actually. They kind of course, they think very hard about this issue because you, what you can have is just actually electric signal and it happens so late. But actually, you should imagine in the cell a lot of process happens here. And finally generate this electron response. So, the is actually, there was a lot of biochemical actions happening in the cell when you have stimulation. We mentioned, what's the steps? The reduction activation you need it some time for the activation to happen. The the confirmation change takes time. And then the activation of the G-protein also takes time. And with the G-protein to activate PDE. PDE hydrolyzed CGMP. All this takes times. [FOREIGN] That the one that has slow kinetics, right? But at the same time, they're found actually this series very sensitive. It just gives a little light. Then this cell can be with a huge response. That is actually, they also found a higher amplification of the cell. Because a G-protein cascade, you have about 20,000 amplification. We talked about, from one Rhodopsin, you can act to maybe around 20 G-protein molecules. And 1 PDE, you can hydrolyse about 1,000 cGMP molecule. So, in the last lecture, we'll talk about actually the sensitivity of our visual system. How sensitive we talk about actually to the eye can perceive with the light. You need how many photons?
