- Neuron membrane potentials questions
- Neuron membrane potentials questions 2
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Explore the neuron resting membrane potential, a stable charge separation across the cell membrane. Discover the roles of anions and cations, and how their concentration differences create this potential. Uncover how neurons use these electrochemical driving forces to perform their functions. Created by Matthew Barry Jensen.
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- I thought the resting neuron mV was -70 not "roughly -60." Is this the case?(16 votes)
- Every text saying something around the range of (-70)-(-60) mV. It depends on what you are looking at. Here are some examples. Personally, I frequent the -70 answer more often than not.
- Describe the cell at resting potential. What is occurring? Which ions are involved(1 vote)
- During resting potential, the cell actively maintains its "inner negativity" (pun intended) by actively transporting ions using the Na+-K+ pump (sodium-potassium pump) which pumps out 3 sodium ions for every 2 potassium ions let in. You can remember it this way:
Na+: "May I come in?" Neuron: "Nah."
K+: "May I come in?" Neuron: "'K"*
The average voltage difference during resting potential is *-70mV.
The Na+-K+ pump is a antiporter.
I really hope this helps you. I know this is a rather short description for a rather in-depth subject so feel free to ask for further clarification!
Edit: Organic anions and other anions (like Cl-) are also important. Sorry I didn't discuss them originally.(20 votes)
- At1:10, Is the neuron is double walled as outer membrane get positive charge and inner membrane get negative charge?(5 votes)
- So, the membrane is a lipid bilayer (so there are two layers of lipids that form the membrane) but the charges on the actual membrane layers are not different. What he is referring to in the video is the idea that there will generally be more freely floating cations outside of the cell and there will generally be less freely floating cations on the inside of the cell. Because anions and cations cannot just flow through the lipid bilayer, this establishes an electrical gradient where the inside of the cell has a more negative charge when compared to the more positive charge outside the cell. However, this is more due to ions than it is due to membrane proteins.(7 votes)
- What would happen if the threshold is the same as the neurons resting potential? A constant firing?(2 votes)
- The resting potential of neurons is about -70 mV. At resting potential concentration of ions is kept constant through Na+/K+ pumps. When the threshold is reached, the Na+ gated channel are opened. The threshold level is about -55 mV. So, the resting potential and threshold can not be same, because of the channels and the pumps that maintain the ion concentration and voltage inside and outside the neuron.(2 votes)
- If there is both a charge gradient and chemical gradient pushing organic anions outside of the neuron, how do they accumulate within the neuron to begin with? Is it during the formation of the neuron?(2 votes)
- The organic anions are often negative charged proteins, which are, if I recall correctly, produced inside the cell. They are too large to leave it through the channels in the cell membrane.(1 vote)
- At1:40, I thought there were still more cations than anions - due to the amount of k+ ions. I thought it was only negative inside relative to the outside?(1 vote)
- So what exactly starts an action potential?(2 votes)
- A graded potential is something that is an input that occurs in the input region. If there is enough excitatory input and it can travel past the decay of temporal and spatial decay, it will reach the axon hillock where it will be determined to send the signal dow the axon by action potential.(1 vote)
- Diagram the connection between two neurons include the presynaptic neuron the postsynaptic neuron synaptic terminals synaptic vesicles synaptic cleft and neurotransmitters(0 votes)
In this video, I want to describe the neuron resting membrane potential, which we often just call the resting potential for short. So first, let me just draw a neuron that'll be a little distorted, just so I have room to draw. So we'll draw this soma here and a really big axon coming out of the soma-- and normally an axon is a thin, long process coming out of the soma, but I just need a little room to draw. So I'll draw a big, thick one. And this will be the other part of the soma, or the cell body. And then I'll just draw one really big dendrite. And like the axon, of course, these are normally just these little thin processes coming out of the soma. But I just need some space. So most neurons at rest, meaning when they're not receiving any input, have a stable separation of charges across the cell membrane called the resting potential. And that consists of more positive charges in a layer on the outside of the membrane, and more negative charges in the layer along the inside of the membrane. And these charges are ions. So the negatively charged ions that are in a layer along the inside of the membrane we also call anions. And the positively charged ions in a layer on the outside of the membrane we call cations. And this layer of anions on the inside and cations on the outside goes all over the neuron cell membrane. All through the membrane of the dendrite, and the soma, and all along the membrane of the axon. And just to be clear, there is a mix of anions and cations on both sides of the membrane. And I've just drawn plus signs on the outside of the membrane to represent that in the layer against the outside of the membrane, there are more cations and anions. And I have drawn negative signs on the inside of the membrane to represent that in that layer, there are more anions than cations. And talk about the size of the difference in the separation of charges, the convention is to call the outside zero. So we just say the outside is zero, and we just kind of set that as the reference. And then we just refer to a single number on the inside of the membrane, which is the difference between the voltage on the outside and the inside, or the difference in the strength of the charge separation. And this difference can vary between neurons, but around negative 60 millivolts would be a really common resting potential for a neuron. So I'll just write a little m and a big V for millivolts. That's the value we use to quantify this difference in charge separation. And around negative 60 would be a really common resting membrane potential for a neuron. The resting potential of neurons is related to concentration differences, which are also called gradients, of many ions across the cell membrane. So there's lots of different ions that have high concentrations outside the neuron compared to lower concentrations inside the neuron, or vice versa. But a few of these ions are the most important for neuron function. The cations, or the positive charged ions that are most important for neuron function are potassium-- and I'll just write that as a K+, sodium, which I'll write as an Na+, and calcium, which I'll write as a Ca2+. Because each calcium ion has two positive charges. And the most important anions for neuron function, or negatively charged ions, are chloride, which I'll write as Cl-, and then there are multiple organic anions. And so I'll just write OA- to stand for organic anions. And there a bunch of different organic anions inside neurons and other cells. Most of these are proteins that carry a net negative charge. Now, these five kinds of ions are going to have concentration differences across the cell membranes, which we also call concentration gradients. And it's different for the different ions if they have a higher concentration inside or outside the neuron. The organic anions and the potassium ions have a higher concentration inside the neuron than outside. So I'll just represent that by having these letters written large inside the neuron. And then I'll write a small OA- to show that there's a smaller concentration of organic anions outside the neuron than inside. And the same for potassium. I'll write a small K+ outside the neuron compared to a large K+ inside, because the concentration of potassium is higher inside the neuron that outside the neuron. And the opposite is true for these other three ions. So the concentration of sodium is much higher outside the neuron than inside the neuron, as is the concentration of calcium. There's much more calcium outside the neuron than inside. And the concentration of chloride ions is also much higher outside the neuron than inside the neuron. Each of these ions, therefore, is going to be acted on by two forces that try to drive them into or out of the neuron. The first is an electrical force from the membrane potential. Because each ion will be attracted to the side of the membrane with the opposite charge, opposite charges attract each other and like charges repel each other. So if we look at each of these ions in turn, the organic anions are negatively charged, so they will be attracted to the outside of the neuron where there are more positive charges. So the electrical force acting on the organic anions will try to drive them out of the neuron. Potassium is the opposite. It's positively charged. So it will be attracted to the inside of the membrane where it's more negative. So it's electrical force will try to drive it into the neuron. Sodium is the same as potassium. It's positively charged, so it will be attracted to the more negative inside of the neuron. Chloride is an anion like the organic anions, so its electrical force will try to drive it out of the neuron. Calcium is a cation like potassium and sodium, so it's electrical force will also try to drive it into the neuron. But now the second force acting on these ions can be thought of as a diffusion force, or it's often called a chemical force, related to the concentration gradients across the neuron membrane. Because particles in solution will always try to move from an area of higher concentration to an area of lower concentration. So if we look at the organic anions, they're in a higher concentration inside the neuron than outside. So their diffusion force will be trying to drive them out of the neuron, just like their electrical force is. Now, potassium is a little confused. Its electrical force is trying to drive it into the neuron, but it has a higher concentration inside the neuron. So it's diffusion force is actually trying to drive it out of the neuron. Sodium has matched electrical and diffusion forces, because it has a higher concentration outside the neuron than inside. Chloride's electrical force is trying to drive it out of the neuron. But because it has a higher concentration outside the neuron, it's diffusion force will be trying to drive it into the neuron. And calcium is just like sodium. Both its electrical and its diffusion force are trying to drive calcium into the neuron. These forces we often call electrochemical driving forces for short. And neurons are going to use these forces to perform their functions. But before we talk about that, in the next video, let's talk about how the resting membrane potential is created and how it's related to the concentration differences of some of these key ions.