Ions - Sodium and Potassium - Video Tutorials & Practice Problems
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1
concept
Electrochemical Gradient
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So in this video, we're gonna be talking about sodium and potassium ions more specifically the force that moves them the electrochemical gradient. Now this is basically a combination of two factors, the electrical gradient and the concentration gradient. So the electrical gradient states a principle that I bet you've heard of before opposites attract. So the electrical gradient makes ions move toward an area of opposite charge. So positively charged ions are attracted to negatively charged spaces and vice versa. Now the concentration gradient states that ions move from areas of high concentrations to areas of low concentrations. So you can think of ions as kind of like introverts. They want to get out of a crowd and move toward an area of low concentration which like same honestly. Now one thing to know about the concentration gradient is that the greater the difference in concentrations of ions between the inside and outside of the cell, the more rapid the diffusion or movement of those ions is going to be so greater difference in concentration gets you more rapid diffusion or more rapid movement of our ions. Now this is sometimes called the chemical gradient. So if you see that people are talking about the concentration gradient. I prefer calling it the concentration gradient because to me, it's more intuitive because it's stating that ions move from areas of high concentrations to low concentrations. But you can call it either one. They're both correct. Now, these two gradients together make up the electrochemical gradient. So these two gradients can be moving ions in the same direction. So for example, they could both be moving sodium ions out of a cell but sometimes they can be opposing. So one gradient could be moving sodium out of a cell and one could be moving sodium into the cell. For example. And if that happens, if they're opposing, whichever gradient is strongest is going to be driving that net flow of ions. So let's just dive right into an example. So here we're going to be drawing an arrow in each of these boxes to indicate which direction the electrical and chemical uh or concentration gradients would be directing the flow of our potassium ions. So just to orient you to this image here we are sitting pretty on the membrane of this lovely neuron. And this orangey area here is our cell membrane, this tan area is our cytosol or the inside of our cell. And this blue area here is our extracellular fluid. And a few things I'm noticing right away is that our extracellular fluid is positive and our cytosol is negative. And I see that we're working with the potassium leak channel, we know all about leak channels, right. These channels are always open and cell and ions can move freely in and out of them. And I see that we have more potassium ions inside the cell. I'm counting six ions inside the cell and four ions outside the cell. So our area of higher concentration is in our cell. So knowing all that information, let's figure out those gradients. So potassium is a positively charged ion and opposites attract, right. So it's attracted to this negatively charged cytozole. And so our electrical gradient would be directing ions into the cell. Now remember for the concentration gradient ions are kind of like introverts, right? They want to get out of a crowd and go from high to low concentrations. So in our case, our area of high concentration is inside the cell and our area of low concentration is outside the cell. And so our concentration gradient is moving ions out of the cell. Now this is a very simplified example. And even though these gradients are opposing, we wouldn't have enough information to know which one is strong enough to drive the net flow of ions. But hopefully you kind of get the idea. So I will see you guys in our next video where we're going to talk even more about sodium and potassium. So I'll see you there.
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Problem
Problem
Suppose the extracellular fluid has a chloride (Cl−) concentration of 120mM, while the concentration of chloride (Cl−) inside the cytosol is 60mM. Also suppose that the total net charge of the cytosol is more negative than the extracellular fluid. Given this information, which statement is correct regarding the movement of Cl− ions?
A
The electrical and concentration gradients both favor movement into the cell.
B
The concentration gradient favors a net movement out of the cell, the electrical gradient favors movement into the cell.
C
The electrical and concentration gradients both favor movement out of the cell.
D
The concentration gradient favors a net movement into the cell, the electrical gradient favors movement out of the cell.
3
concept
Standard Sodium and Potassium Concentrations
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OK. So now that we understand how and why those ions move. Let's take a look at where those ions actually are. And for context, we'll be looking at these ion concentrations in a cell that is at rest. So our neurons not communicating just taking a little break. So when our cell is at rest, what we typically see is that for sodium, we have a relatively low intracellular concentration. So not very much sodium inside of our cell, but we do have a very high concentration of sodium outside the cell. And we see the opposite pattern for potassium. So for potassium in a cell that is resting, we tend to have a very high concentration inside the cell and a low concentration outside the cell. All right. So easy peasy lesson there, right. Let's dive right into our example to kind of visualize this and practice those gradients of it. So what we're going to be doing here is given what we just learned about those sodium and potassium concentrations, we'll be drawing an arrow in these boxes to indicate which direction the concentration and electrical gradients will be directing the flow of these ions. So to quickly orient you to our image here. In case you haven't seen this before. The orange here is our membrane. This tan area is our negatively charged cytosol. This blue area is our positively charged extracellular fluid. We have our pink potassium ion and our little purple or ion, our little pink potassium leak channel there and our sodium leak channel. Remember these guys are always open ions are coming in and out and just looking at these pink and purple sodium and potassium ions, I can see that these concentrations are what we just talked about. So I'm counting 12345 potassium ions in the cell, our high concentration and two outside the cell, that's our low concentration and the opposite pattern for sodium. So I see 12345 sodium ions out of the cell. That's our high concentration and just two inside the cell. That's our low concentration. So let's start with those concentration gradients since we've been talking about that this whole time. So remember ions are like introverts, right? They want to get out of a crowd, go from their high to low concentrations. So for potassium that's gonna be directing the flow out of the cell, right? The high concentration is in they want to get away from that. So they're gonna be going out of the cell. And for sodium, we'll see the opposite pattern. So our high concentration is outside the cell. So they're gonna want to move into the cell. And so the electrical gradients for these are actually going to be the exact same because they're both positively charged ions and remember, opposites attract right. So they're both attracted to this negatively charged cytosol. And so for both of these ions, the the electrical gradients will be directing the flow into the cell. All right. And you can see kind of a nice example here of what I mentioned in our last video how sometimes these gradients can be opposing and sometimes they can be more synergistic. So for our potassium, we have these opposing gradients with the concentration gradient directing the flow out and the electrical gradient directing the flow in. And this is a cartoon obviously we don't have enough information to figure out which one is stronger and would drive net flow. But it gives you kind of a nice idea and a nice comparison to sodium here where both gradients are directing the flow into the cell. So you can tell we're going to have a pretty strong net flow of sodium. Huh. All right. So that is the sodium and potassium concentrations of a cell that is at rest. And I will see you guys in our next video.
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Problem
Problem
In a neuron at rest, the concentration of __________ is higher outside the cell than in the cell, whereas the concentration of _________ is greater inside the cell than outside.
A
Sodium; potassium.
B
Potassium; sodium.
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Problem
Problem
Which of the following statements is true regarding how the concentration gradient affects sodium ions when a cell is at rest?
A
When a cell is at rest the concentration gradient has no effect on sodium ions.
B
The concentration gradient drives sodium ions into the cell.
C
The concentration gradient drives sodium ions out the cell.
D
In a cell at rest the electrical gradient moves into the cell.
6
concept
The Sodium Potassium Pump
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OK. So up until this point, we've talked about how ions can move passively via their electrochemical gradients. But you guys may remember that's not the only way that ions can move. Like we talked about way earlier in the course, active transport can move ions against their electrochemical gradients. And they do this via a TP consuming pumps. Now, arguably the most important a TP consuming pump in the human body. And my personal is the sodium potassium pump or the sodium potassium A TP A. Now, this pump works by ejecting three sodium ions from the cell. So they get kicked out and it transports two potassium ions back into the cell. So it's basically moving those ions against those natural gradients. Remember when our cells at rest, our leak channels are open, sodium wants to leak in and potassium wants to leak out. And our pump says uh uh and it kicks that sodium back out and it pulls that potassium back in. So if we're looking at our figure here, we have our lovely blue pumps and you can see here three ions are being ejected from ourselves. So that's got to be our sodium. I'm gonna label each of these as sodium. All right. So they're getting tossed out and I see two ions here getting pulled back into this C is all that's got to be our potassium. So I'll label that as potassium. Now, it is very important for you to understand how this pump works and what this pump is doing. So to help you do that, I have some fun memory tools. Now this one I can't take credit for. I first saw this in Jason's General bio class and it was so stinking cute. I had to take it. So the idea here is to imagine our neuron as a club. This is club in Intercellular club in Intercellular is located in the salty salty sea of the extracellular fluid full of sodium, right? So we're in club Intracellular, there's music, there's lights, we're dancing. We're being responsible though and we have our bouncer. The bouncer is the sodium potassium pump because this guy works a lot like a bouncer. He decides who gets in and who gets out, right? So what our bouncer is gonna do is he's guarding the door and these three sodium ions are gonna come and they're gonna be like, hey, can we come in the club and he's gonna tell them nah because sodium is N A, right? So cute. And then these two potassium ions are gonna come and be like, hey, can we come in the club and he's gonna tell them OK, because potassium is K so cute. Full credit to Jason. Love that. So that's a super fun way to imagine it if you prefer less elaborate study methods though. Um My favorite, easy, easy peasy way to remember this is to just write out sodium as N A plus and potassium as K plus and then just count the characters. So N A plus is three characters and K plus is two characters that helps you. Remember we're working with three sodium and two potassium. My other favorite easy way to think about this is to remember a pumpkin. So just draw yourself a little pumpkin or something because remember we pump the K potassium into the cell and whatever we're doing to potassium, the opposite is being done to sodium. So kind of an easy way to help you remember that. Now I'm giving you all these tools because like I said, it's important to know how this pump is working. It's gonna come up a few more times and so be sure to take your time with this study it and I'll see you guys in our next video to talk more about the function of our sodium potassium pump. See you there.
7
example
Ions - Sodium and Potassium Example 3
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1m
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All right. So let's run through our example. So our example reads, Terry was injected with a poison that blocks the sodium potassium pump with the sodium potassium pump blocked what will happen to the concentration of potassium inside the cell? All right. So let's just kind of draw this out so that we remember what's going on. So in a cell, we have higher concentrations of potassium inside and higher concentrations of sodium on the outside, right? Which means that potassium following its concentration gradient wants to leak out of the cell and sodium wants to be coming into the cell. And our pump is working to kick that sodium back out right? And bring that potassium back in. OK. So that's what's going on. And now that that's kind of fresh in our head, let's think through these answer choices. So a reads that if the pump was blocked, the concentration of potassium inside the cell will increase. And that can't be right. Huh. Because if we just have potassium leaking out and there's nothing replacing it, it's definitely not gonna increase. So A is out B reads the concentration of potassium will decrease and that is correct. So B is our answer. So if potassium is just leaking out and there's nothing replacing it, it's gonna decrease over time. Huh? So let's just really quickly go through C to make sure that we understand why it's not correct. So C reads that the concentration of potassium will be unaffected. And that's just not true because like we just talked about potassium wants to be leaking out and now there's no pump replacing it. And so the concentration is certainly being affected in that it is decreasing, right? So C is incorrect as well, right. So our answer is b the concentration of potassium will decrease and there you go.
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Problem
Problem
Which of the following statements about the Sodium Potassium pump is correct?
A
The sodium potassium pump operates as a mechanically gated channel.
B
The sodium potassium pump transports 3 potassium ions and ejects 3 sodium ions.
C
The sodium potassium pump always helps ions move down their natural electrochemical gradient.
D
The sodium potassium pump transports 2 potassium ions and ejects 3 sodium ions.
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