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0:01
S Sun: Hi, guys, welcome back. Alright. So S Sun: we continue our lecture and to talk about the membrane potential. S Sun: So memory potential basically is is about that. Let me let me show you what is memory potential. So when we in in in S Sun: a and b anatomy, physiology. S Sun: one thing you need to keep in mind is always like when you learn about the terminology, a new terminology. You always think about 2 things location and the function. Where is it? And what S Sun: does it do?
0:42
S Sun: So where is it? Membrane potential is a membrane. So it's right here. So here is the membrane set also means that inside of cell. And this is outside of cell plasma membrane we mentioned about that this is the cell membrane. S Sun: the barrier surrounding the cell. S Sun: And so you can see that if you put the electro inside outside, you see that it's always inside is always negative. Outside is like share shared space between cells. So we consider this as the the ground, like
1:18
S Sun: we, it's the common ground of all other cells or all cells. And for each cell we measure what is inside, and so we can measure it as negative. And you will see this throughout the every cell in the human body, that inside of the cell. The charge is negative somewhere, like minus S Sun: 50 or 60 mini mode. Mv, yeah. So that is what we got. So this memory danger. S Sun: So location is on the memory function.
1:57
S Sun: It's a phenomena. It's just, and it will become quite important. This is a foundation for electrophysiology. S Sun: And in that thing, in the, in the in the human. S Sun: in the organism is based on this. S Sun: So this is important. So that's memory. We are going to talk about that
2:21
S Sun: before we talk about that. I want to review one thing that we just mentioned earlier, which is the active transport. So that is this thing here. S Sun: this thing here, so sodium, potassium pump.
2:34
S Sun: Every cell, as I mentioned before, every cell has this pump. S Sun: so every cell will have this pumped to do one thing, pumping sodium and pumping potassium in addition.
2:49
S Sun: 9th addition. So that's that. All right. So it pump in sodium pollutant magnesium. We need to know that it pumped 3 out pump 2 in S Sun: pump, 3 sodiums out pump, 2 potassium C,
3:05
S Sun: these pumps will result in 2 consequences. S Sun: One is that you're gonna accumulate sodiums outside of cell. And you're gonna accumulate potassium inside of cell. So let me draw it again. Right here. Let me use my S Sun: tool pencil to draw it again. Right here. I already have my pencil. So this is a cell. S Sun: So with this pump, it will lead to one consequence. The 1st consequence that you're going to accumulate potassium in South Cell. S Sun: But I think it means upsell
3:41
S Sun: sodium outside. It cannot flow away. So it's out. It's gone. S Sun: Are you going to accumulate potassium in self sale. Okay, you can put sodium outside. That's fine sodium. S Sun: Everything is outside, everything else is outside. S Sun: But potassium is inside. Yeah. So you trap potassium inside of the cell. S Sun: So that's verdict. You trap the inside cell.
4:07
S Sun: Second thing is that you can see that sodiums and the potassium are positive charged Ion. So these are positive charge. These are positive charge positively charged. S Sun: So you have more positive charge to push out, and you only push in less positively charged. Ion. So you have 3 out, 2 in, 3 out, 2 in. So gradually you have 3 out, 2 in 3 outs, 2 in 3 outs, 2 in. Gradually. You build that diversity you build, that polarity S Sun: differs.
4:47
S Sun: and so inside is not so much. But you have more positive outside. So you create that polarity inside is not so much. S Sun: But you add more positive outside. S Sun: So that's that. So that's a second consequence, because these 2 numbers are not the same. 3 out, 2 in. S Sun: Yeah. So that's that this gave the foundation. That the membrane is not equal. The charge
5:20
S Sun: across the memories are not equal inside is not S Sun: is relatively more negative, and outside is relatively more positive. S Sun: That is the sign of a living cell. A living cell has the atp, a living cell going to pump S Sun: a living cell, gonna create a negative memory potential. S Sun: So that's that. If is, if it's if you don't see that charge difference. If you don't see that polarity. S Sun: This cell is a dead cell. Yeah. S Sun: So that's the foundation.
5:59
S Sun: So that's that memory potential is driven by sodium, potassium pump. S Sun: Oh, I forgot to mention sodium potassium pump is also called sodium potassium adps. I mentioned here. S Sun: Sodium potassium pump is also called sodium potassium adps, because it require adp S Sun: ace means like license, it break apart the atp, utilize it to do its work.
6:32
S Sun: So that's that. So this one basically is single-handed.
6:37
S Sun: create memory potential. So further thing is that we can see that the distribution S Sun: between intracellular space versus extracellular space. You can see a lot of things here, different kinds of the ion different kind of ions, but the only thing you need to memorize is that S Sun: potassium is high inside of cell S Sun: right here. Potassium, see potassium very low. Potassium is high inside the cell. S Sun: Everything else are outside. So that's very simple.
7:14
S Sun: Everything else are outside inside of cell. You have capacity because of this sodium potassium pump.
7:25
S Sun: Second thing is because the number is different, 2 k in 3 NA plus out. S Sun: the number is different. So you create that negative relatively negative charge inside of cell relative to the extracellular space. S Sun: So that's what we got here. S Sun: Every cell, every human cell has a sodium potassium pump as sodium, potassium pumps.
7:51
S Sun: The consequence is that it gonna lead to a negative charged membrane potential in a cell. So every cell with the skin with that nerve, whether that's blood cells. You're going to see the membrane potential to be negative. S Sun: So that's that very simple right memory potential.
8:15
S Sun: The next thing that we are going to learn is that? Alright? So every cells has a negative memory potential.
8:24
S Sun: But some cells are.
8:28
S Sun: I have more than that has more than that. S Sun: Some other cells will utilize this to do different things. S Sun: We call this group sales excitable sales is that now the main potential is negative. Right? You have more positive outside. S Sun: relatively more negative inside. Some Rsl will use it to do some manipulation. S Sun: and the big and and the 2 to performance function we call this cell are excitable cell. They can be excited.
9:04
S Sun: Excival sales. There are many, but general speaking S Sun: nerve cells, and the muscle cells are excitable cells. Yeah, they can get excited
9:16
S Sun: when they get excited they will change the memory potential. S Sun: they would natureize it, they would depolarize it. So this is polarizer S Sun: right? They would depolarize, make it make it neutral, make it equal. S Sun: and then that will show a signal to surrounding things.
9:45
S Sun: and then they will return back to negative again. S Sun: so they can depolarize it and then repolarize it. S Sun: And this action, this action is called action potential. S Sun: Yeah, so excitable cell will change it to S Sun: to create an action potential. So let's take a look.
10:09
S Sun: Every cell has a sodium-potassium pump. S Sun: but excitable sales has 2 more things. They are. S Sun: They have, in addition to the sodium potassium pump. They also have voltage-gated sodium channel and the voltage gated potassium channel. S Sun: So that's 2 other things, sodium potassium pump S Sun: lay the foundation of a negative membrantial S Sun: voltage-gated sodium channel and voltage-gated potassium channel. Allow these cells to generate action potential.
10:48
S Sun: Yeah. So so let's take a look. So this is a figure of this exponential. So you can see that S Sun: this is time. S Sun: So sales, you know. Times goes on. S Sun: Cell is not excited. S Sun: The memory potential will be negative, say, minus 70 minivolt. So it's negative. S Sun: right? Time goes on. It's always negative. S Sun: Now, when you excited. S Sun: If this can be excitable.
11:19
S Sun: then it will generate activity, so you can see that its member credential will change from negative to be S Sun: 0. S Sun: If something's overshoot, a little bit. S Sun: depolarize, it was polarized. Now it depolarized. So this phase is called depolarization.
11:40
S Sun: and then very quickly it will return back to S Sun: polarization. So we call it repolarization. So we have the depolarization. When you excite it S Sun: above a threshold. You need to excite it. You need to stimulate it, sure enough S Sun: to move above the threshold, then it will trigger its depraization. S Sun: Everything like it was porous, become neutral. It sounds overshoot a little bit.
12:11
S Sun: and then recordation. So it's excited. S Sun: Come back and coming coming out and back, coming out of that. Yeah. S Sun: So that's so, that's action potential. This one is driven by these 2 membrane protein. You got to have a voltage radius. Only channel S Sun: is gated. S Sun: It allows sodium S Sun: to go through is gated by the voltage. So this voltage is the charge on the membrane. S Sun: You also have another one voltage-gated potassium channel.
12:46
S Sun: So this channel allow potassium to go through and is gated by the membrane charge. So that's that. S Sun: And the action potential. You basically has S Sun: depriation. 2 major phase. You have a deprization phase, and then you have the reparization phase. S Sun: So 1st is that you need to stimulate these cells above a threshold. So stimulation is needed to initiate this action potential. S Sun: and this stimulation has to be above the threshold. Once it's above the threshold.
13:26
S Sun: then you trigger it. It will create a deprization S Sun: very short period of 1 ms. S Sun: followed by very quick return back to the baseline reparization. S Sun: So deprization is driven by here threshold, so you can stimulate it, you can poke it. S Sun: but if it's not above threshold, it's just coming out and back, coming out back. So it's not. It doesn't generate the depolarization. It doesn't really depolarize it
14:02
S Sun: only until your stimulus stimulus is above the threshold. Then you trigger its deputization and the reprodization so S Sun: just like your touch, right. You stimulate it. S Sun: and it has to be strong enough. S Sun: So it trigger action potential. Then you can transmit that signal S Sun: into your brain. So you can. S Sun: You can receive that touching sensation. Right?
14:35
S Sun: Then you have the depriation. Deprisation is by driven by voltage, radius, or internal. So you cannot. S Sun: So basically, that this channel right here. So here is the sodium channel. All right. So you have the voltage gated sodium channel. S Sun: You avoid. You get the potential when you're when your membrane is stimulus. S Sun: The charge change. It increased a little bit, but it's not too much, however, that increase. If if it's above the threshold.
15:09
S Sun: your voltage gate Isolian Channel. S Sun: Gonna pick it up, and when it picked up this channel will open.
15:19
S Sun: When this channel open it will allow sodium to go through. All right. So let's go kind of like review of what we have learned. This is a facilitated diffusion. S Sun: A channel sodium sodium will go through by diffusion. Diffusion is a movement of the molecule from high concentration area to low concentration area. Now, when this channel open, you have a cell. S Sun: you have this channel.
15:53
S Sun: When this channel open. It allows sodiums to go through all right, so sodium sodium can freely diffuse across. Now
16:01
S Sun: Julian can go through. S Sun: Yes, so. S Sun: And this movement is moving from high concentration to low concentration. So you have. You kind of have to decide right? You can kind of like, ask yourself, will sodium tend to move in more or move out more. And the question is. S Sun: basically, where do we have higher concentration of sodium? Is that outside, or is that inside? S Sun: And the answer is outside, right? So we know that inside you only have potassium. So sodiums is more is
16:36
S Sun: is our outside. So you have a lot of sodiums outside. And so when this channel opens, sodium will S Sun: brushed in like S Sun: coming in right? So they will come in because they're going to move from high concentration to low concentration. S Sun: And with this sodium coming in sodium, bring a positive charge, Ion. They're gonna make insight to be very quickly to be positive, so that S Sun: depolarize it. S Sun: Remove that negative environment to become positive. Okay.
17:10
S Sun: yeah. So that's deposition is driven by voltage. Gated sodium channel sodium will influx S Sun: from outside to inside of a cell. S Sun: and and then this channel close very quickly
17:31
S Sun: when the channel, when when the memory potential reached to that S Sun: 0 or a little bit positive.
17:40
S Sun: Then potassium channel open, and so right here. So S Sun: when potassium channel open again right here. So a cell S Sun: you have the voltage gated potassium channel right here. S Sun: So again, here you have the voltage gated potassium channels. S Sun: This is again a facilitated diffusion. So the question is it allow potassium to go through. So this allow potassium to go through.
18:10
S Sun: And then we need to know. We know that molecule move from high concentration to low concentration. So the question is, where do we have high concentration of potassium? And we know that inside of cell you have high concentration of potassine. Right here
18:29
S Sun: you have a lot of potassium inside the cell. S Sun: So when this channel open. S Sun: a lot of potassium will go out right, so you will diffuse out. You will diffuse out. You will diffuse out. S Sun: and when it diffuse out, this is a positive charged Ion. It will make inside to be negative again. S Sun: and so it it caused the main financial to become negative, it caused inside to be negative. S Sun: it, repolarize it, make it polarize again.
19:12
S Sun: And so this is the reparization phase is driven by voltage, gated potassium channel, and with this channel open S Sun: potassium will move from intracereal space to extracellular space. S Sun: So, like you see here this voltage, Gadian Channel, it opens, but nothing goes out. S Sun: This is a concentration gradient from high concentration which is inside to low concentration, which is outside.
19:44
S Sun: So that is great. Summarize everything you need to know about the action potential. So this one summarize it.
19:55
S Sun: Before any excitement, any stimulus S Sun: cell, maintain a negative memory potential. S Sun: You have negative charge inside of cell S Sun: positive chart. Here it shows neuron. Neuron is an example of the excitable cell. S Sun: And so you can see it's a negative inside positive outside. You have more. You have more potassium channel. Sorry potassium ion in the cell, and more sodium ion out of cell
20:28
S Sun: when you stimulate it. The 1st thing you see is a sodium channel sodium right here. Sodium channel open sodium channel open S Sun: when Sony channel open S Sun: voltage, gated sodium channel open right here. Voltage gated sodium channel open. This one is 1st of all, the resting memory potential is driven by sodium, potassium, and eps. So you have this pump causing S Sun: high concentration, potassium intracellularly, and also memory memory potential to be negative.
21:03
S Sun: When you stimulate it, you trigger, you change the charge. You make it a little bit like it's not a lot, but you stimulate it. S Sun: and that can be picking up by voltage gated sodium channel. And this channel will open. Then it allows sodium to go through freely. S Sun: and the constraint with low concentration, so sodium will go in. Sodium will go in. S Sun: and then it will bring the positive charge into the cell. And so it caused deprisation. So it was
21:36
S Sun: negative, and then here, passive, right positive, coming in negative and positive coming in, and then it close. S Sun: Then you have the reposition. Basically, it's driven by the Voltage Gate S Sun: potassium channel. You will see that it will coming back because this channel open potassium freely diffuse across S Sun: from high concentration to low concentration. Well, they move out. They bring this positive charge out S Sun: out of the cell to make it
22:16
S Sun: make the inside to be negative again. S Sun: And so it's re re means regain that polarization. S Sun: And then because and then you have this sodium potassium pump. S Sun: 2 maintain or to create S Sun: the resting memory potential, which is negative throughout our body. Yeah. S Sun: So that I think that summarize everything we need to know. I think this is a last picture, maybe not last. But here is a summary again.
22:59
S Sun: So this is the exponential. Before you stimulate it is remain as a resting member, financial which is always negative. S Sun: Question is, what caused it to be negative. And at this point you should know that the S Sun: the the things to cause a memory potential to be negative is because S Sun: sodium, potassium pump, and every cell has it.
23:30
S Sun: Now, when you stimulate it, it was weak stimulus. S Sun: It won't cause any change. It won't stimulate an action potential. S Sun: But if it's strong enough to push it above the threshold. S Sun: then you're gonna trigger a voltage sodium channel sodium. Go in causing depolarization S Sun: very quickly. It grows, followed by voltage. Gated potassium channel open. S Sun: allow potassium to go out out and then driven the reprisation.
24:11
S Sun: and then, when it goes out sometimes wrong too fast. Make it S Sun: too negative. And then it's called hyper. Too much S Sun: polarization. Hyper means too much. Polarization means it's porous. S Sun: But you have this sodium potassium pump to gradually regain them into the resting memory facial.
24:35
S Sun: We see this actual potential in the excitable cells and 2 major cells, 2 major type of cells that are excitable are nerve cells and the muscle cells. S Sun: So I think in my last slides, I'm gonna show you S Sun: the application or this scenario in a nerve cell. So here I show you the nerve cell.
25:05
S Sun: a nerve cell. In our nervous system lecture. We kind of go through. S Sun: What a nerve cell look like a nerve cell basically has a cell body. It's called Soma and an axon. S Sun: So this membrane is negative has a negative membrane potential. But if if it's received the stimulus S Sun: like your touch, like you see something or you smell something acting on it, you're gonna trigger
25:39
S Sun: the action potential. So it will get deprised. So you can see that in the beginning is negative. Inside S Sun: is resting memory potential. But when you stimulate you 1st trigger the voltage gated sodium channel. So you cause it deprisation with this deprization. S Sun: even though it's just locally allow sorry. Allow Sodians to go in. S Sun: Let me join here allow Estodian to go in main. S Sun: even though it's very locally allow sodium to go in. This sodium cannot diffuse
26:21
S Sun: across, and when it diffuse across it, gonna trigger an action potential. So this action potential gonna propagate S Sun: from the Soma. S Sun: from the location where they receive the stimulus all the way into the external terminal. So you can see that deputization reparization, this gonna S Sun: propagate from the beginning of the Exon toward the end of the axon. S Sun: Yeah. So so we call these we call these nerve impulse. S Sun: You need to know. Nerve exome is very long.
27:03
S Sun: For example, when you touch something. S Sun: this nerve has axon. Go all the way into your spinal cord. So you do. S Sun: can you? You definitely can use your electro to detect this impulse from your finger S Sun: and to see its transportation to your spinal cord.
27:33
S Sun: So so that this nerve impulse is is is best to describe the action potential traveling. S Sun: Along the axon, basically, yeah. S Sun: along a neuron. But basically it's along the axon. S Sun: Well, that's that. S Sun: And then so you can deliver that signal. Say, this is the end is they say fragment. Right? So you put perfume on S Sun: fragment, bind on it. S Sun: bind on it, and then it trigger action potential. This one will go into your brain so you can smell it.
28:13
S Sun: So that's how you deliver that signal. On one end. You receive that stimulus S Sun: in the Axon terminal. It will tell S Sun: it into your brain because that action potential gonna travel down there. S Sun: Yeah. And this transportation is very fast. Yeah, so that ends our lecture S Sun: and hope it helps you to understand S Sun: the importance of the cell membrane S Sun: and also from there to understand the memory potential and the action potential.
28:50
S Sun: Let me know if you have any questions. S Sun: I will see you next time. Bye-bye.
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