Ion Channels and Neurons - Online Tutor, Practice Problems & Exam Prep

Neurons transmit signals through action potentials, which are rapid electrical impulses generated by voltage-gated cation channels. When a neuron receives a signal, sodium channels open, causing depolarization. This triggers further ion channels to open, propagating the signal down the axon. At the nerve terminal, the electrical signal converts to a chemical signal via neurotransmitters, which bind to receptors on the postsynaptic cell, initiating new action potentials. Neurotransmitters can be excitatory, like acetylcholine, or inhibitory, like GABA, influencing neuronal response and synaptic plasticity.

Neuron Structure

Hi. In this video, we're going to be talking about ion channels, action potentials, and neurons. The very first thing that we need to discuss before we go over anything related to neurons or signaling is the structure and anatomy of a neuron. This video will essentially be a vocabulary list of different structural features of neurons. So, bear with me. Neurons are nerve cells that function by receiving, integrating, and transmitting signals. They have a few distinctive physical features. One is the cell body. I'm going to try to go over this as I describe them. Let me back up. The cell body, also sometimes referred to as the nucleus, is the core of the neuron. You're going to see the cell body here. This is the cell body. Then you have your axons, which are the long extensions that conduct electrical signals away from the cell body. If we're looking at what the axon is, it's this long structure here. An interesting thing about the axon is the diameter, which kind of controls the speed. The larger the diameter, the faster the speed. That's interesting. Then you have your dendrites, which are several shorter branches that radiate from the cell body to receive signals. If we look where our cell body is, here we have our dendrites. Oh, let me use a different color. Our dendrites extending here in various ways, and then we have the nerve terminal. So here, dendrites, And then we have our nerve terminal, which is going to be the end of the axon that branches to pass messages to whatever cells at the end of it. So your nerve terminal is going to be here, sometimes called the synaptic terminal. That's the first four, then I'll move on.

Now we're focusing on some vocabulary referring to axons. Axons can take distinctive features as well. One of these features is called myelin, which is going to be a protective covering that forms around the axon. Some of the cell types that are found in this are known as glial cells or Schwann cells. Just in case you see those cell types in your book, know that those make up the myelin. The myelin sheath is responsible for insulating the axon so that ions passing through the axon can't leak out of the membrane and wreak havoc in the body. Finally, there's another term called the node of Ranvier, and these are actually just patches of ion channels that interrupt the myelin sheath and are really responsible for neuronal signaling. The signal is passed between these nodes of Ranvier down a neuron. We're looking at what this looks like. Remember, we're focusing on the axon, which is going to be this long terminal here. You can see that there's this myelin sheath, this blue covering here that protects the axon from leaking out ions, but it still does need to be able to import and export ions. So you have these nodes of Ranvier here that are interspersed, sort of, groups of ions.

Finally, let's talk about the junction between the neurons, which also contains distinctive physical features. The terms here that you need to know are synapse, which is the junction through which the signal is transmitted. That is going to be this region here, the synapse. Then you have the presynaptic cell and the postsynaptic cell, which are the cells that either have the signal and release it or the cell that receives it. You can see here the presynaptic cell has the signal, and it releases it into the synapse. The synapse, or synaptic cleft, then allows the postsynaptic cell to accept it. Finally, you have the synaptic cleft, which is the space between the pre-and postsynaptic cells, which is what I referred to as the synapse here. You can also call it the synaptic cleft. Technically, the synapse can refer to the whole thing, the presynaptic and postsynaptic cells, and then you have your synaptic cleft. I know that's a lot of vocabulary, so bear with me. Maybe review the video a few times until you get all that vocabulary down. So now let's turn the page.

Action Potentials

Okay, so now we're going to talk about action potentials. Essentially, action potentials are just these waves of an electrical impulse, which carries a message from the neuron. I like to think of this as kind of the electrical wires that you may see around cities, or they may be buried underground. But we all know that electricity gets to our house because of electrical wires. What those wires do is they send electricity from the power company to our house. Neurons are exactly like that, except that the electrical impulse isn't just pure electricity; it has a message with it. It's supposed to do something, and it comes from our brain to wherever it's supposed to go. So if we're touching something hot, then our brain triggers this impulse saying, "hey, that's hot. Move your hand." That travels through our neurons from the brain to our hand and causes the muscles and the bones in our hand to move. Action potentials control that. The action potential is that actual sort of electrical pulse that is being sent through the neurons so that our brain can communicate with other parts of our body. You can imagine that this is super fast. Fast. Because when we touch a hot stove, there's not a delay from the moment we touch it to when we move our hand. It's almost instantaneous. We feel it's hot. We move it. And it's because these electrical impulses that are passed through these neurons, these action potentials, are so fast; they travel up to 100 meters a second, which is, I mean, almost unimaginable. That's how fast they move. And importantly, not only are they moving fast, but they also do not weaken the message, which means when we touch a hot stove and our brain realizes that it's hot, then it's not that the electrical impulse slowly travels from our brain to our hand, it gets weaker and weaker until we just think it's warm. No, it's hot, and we know it's hot, and that message does not ever weaken in the time or the distance it takes to travel from our brain to our hand. So, it's fast, and it is strong, these messages that are transported through neurons. And these messages are what we call these action potentials because they're electrical messages that get sent. So, what causes an action potential? An action potential is this electrical impulse that travels from our brain to our hand or wherever else, but something has to actually cause that. We have to generate this electrical impulse. So what generates that? The thing that generates it is called a voltage-gated cation channel. We've gone over terms of different transport channels before, but let's just remind ourselves what this is. Voltage-gated. So that means that this protein is going to be controlled by positive and negative charges, like voltage-gated. So it's going to open with certain charges, and it's going to close with other charges. It's a cation channel, which makes sense that it's voltage-gated, right, because cations are going to be positive ions. Positively charged ions. And so, this voltage-gated channel is going to be controlled through these positive ions, and they're going to open so that positive ions can move through them. And they are what control this action potential, so they are what controls this electrical impulse, which is good because if, I mean, what is an electrical impulse? It's just these influxes of electrons that are negatively charged, and so, electricity is essentially just these charge differences, and therefore the proteins, these voltage-gated cation channels, are opening to allow positively charged ions to get in. So how does this work to control an action potential? We're going to go over individual steps in future videos, but I just want to introduce it here. What happens is that normally a neuron has a certain charge, and that charge is negative 60 millivolts. And that means that the intracellular space, inside the neuron, is more negatively charged. This voltage-gated cation channel lets positively charged things in. If the inside of the neuron is negatively charged, that means that most of the time this voltage-gated cation channel is closed. It's not letting these positive charges in because as soon as it opens, those positive charges are going to go straight in to be with those negative charges. And so most of the time, these voltage-gated ion channels are closed. But what happens is that there's some kind of trigger. Maybe you're touching a hot stove, maybe you stub your toe, I don't know. Something triggers this cation channel to open. What happens when it opens is all those positive ions come in, and that rapidly changes this charge, the charge that neurons usually used to at negative 60 to plus 40. So, if you go from negative 60 to plus 40 in just a split second, that is a rapid change, and it triggers a lot of things to happen. So if I'm just to draw we'll just say that this is an axon, remember? That's that long part of the neuron that where these signals travel from the dendrites to the nerve terminal. What happens is if the signal, this sort of trigger comes in here, so we'll just say that this is a heat trigger, then we have these cation channels that then open, and that causes a rush of positive ions into this little section of the neuron. Right? But what happens is eventually this trigger goes, and it starts bringing the positive ions to the next one, and that will trigger this one to open. And so these positive ions begin coming in and coming in, and they travel along until they reach the next one where this one will open, and then this will go in. So, now we've started this huge process where all of these are opening, all of these cations are coming in. This is a huge electrical signal that is traveling this way through the axon. So when eventually though, we need to shut off this impulse. Right? Because when we move our hand off the stove, then our brain doesn't need to keep telling us our hand's burning. Right? Because that would stop. We no longer need that message. Well, the only way we can stop that message is if we counteract this positive charge. And so how we counteract this positive charge is through a series of potassium channels. Now remember, potassium is also positively charged, and so, how do we use potassium to get the membrane back to its resting membrane potential, which is negative 60, which is what we started with. So how we do that is that some of these channels open at different times and allow for the positively charged potassium ions to flow out of the neuron, and that really can help get the neuron back to its normal thing. So, there are a few I want to talk about. I want to talk about the delayed potassium channel, and so it is returning the neuron to its original state. So if we have these, these are the voltage-gated channels. And remember, we started, and they're open now, and they're influxing a bunch of cations into the cell. But we also have potassium ions here. And so, these delayed ones open after this one opens. So, if this one opens first, this one will be delayed and open second, and that allows these potassium ions to flow out of the cell. When that does, we're lowering the amount of positive charge here. The second one, so this is really the one that's responsible for getting the positive charge out of the neuron. So it's delayed. It happens after this one opens so that the signal can still be passed, but that we're not just continually accumulating these positive charges. So we have the voltage-gated channel opening first, and then we have a delayed potassium channel to allow those positive charges to get out. We also have another one called a rapidly activating. So obviously, that's going to activate pretty quickly. And, this is a really important one because it controls the relationship of firing to intensity. So what do I mean by that? Well, when we, when these voltage-gated cation channels open and those positive charges rush in, if we allow that to just continually build, that's going to be a huge signal. So that if we're touching a stove, if we just allow those positive charges to accumulate, then, what will happen is that when we realize our hand is touching the stove and our fingers are hot, it will feel like our whole body is on fire. And we don't want that. We don't want to feel like our whole body is on fire when only our hand is touching the stove. So, these rapidly activating potassium channels are making sure that the positive charge inside the axon never gets so much that it's just way too much, way too much intensity. Right? So it's allowing those potassiums to come out of the axon so that we make sure that we have a positive charge in the axon, but that it's not so large as it's just overbearing our entire nervous system. And then, the third really important potassium channel is the calcium-activated potassium channel, and we'll talk a lot more about how calcium is involved in this process when we go over the detailed steps, but just know for now that it is. And this activated channel, what it does is it puts a delay between one action potential and the next. So what does that mean? Is that when we have this we have, I don't want to draw it like that. Hold on. Let me erase this. Okay. So when we have a neuron, this is an axon, and we open this one, and we get lots of positive charges, and that travels to the next one, which causes it to open. Right? Positive charges. And then we have our delay channels, potassium channels, that allow the potassium to come out. And eventually, this will go back to its negative 60, But the calcium-activated potassium channels make sure that there's a delay between this action potential and the one that's going to come after it. So you need that delay, and so there's more potassium that comes out to ensure that the axon gets back to its resting membrane potential, which is negative 60, so that, it will delay from 1 action potential to the next. So I know it's really confusing, we are going to go over individual steps in the future, but what I want you to get from this is what an action potential is, which is just that electrical impulse that's being passed along through the neurons from your brain to wherever it's signaling, like your hand touching a stove. The action potential, those electrical impulses, are controlled through the positive ions getting into this axon, and that's controlled through these voltage-gated cation channels. And then what happens is that there are potassium channels that regulate it. They make sure that it can return to its original negative 60 state in the case of delay. They make sure that the intensity never gets too large for us to handle, and they make sure that we're not just constantly firing and just sending more and more electrical signals through these, just more and more action potentials that say, wait. We'll finish this one before we start the next one. So that's really what I want you to understand from this topic. I know there's a lot of vocab words, and like I said, the individual steps of this, we're going to talk about later. But I just want you to kind of get the overall process of what action potentials are, how the positive charges are really controlling this, and how these potassium channels are really about regulating the different facets of it, whether it's returning to its original state, controlling the intensity, or controlling how fast all these action potentials can happen one right after another. And so, if we were to look at what this looks like, I've now drawn it out a lot, but I like these pictures better because they're much better. What happens is we have some kind of trigger, potentially this is the trigger, which comes in. And now we have the axon, which has all these voltage-gated cation channels right here, and they're opening. And that's causing lots of positive charges to flow through the neuron, and those positive charges that are flowing through the neuron, those are the action potentials. And after they begin to flow through the neuron, what we get is we get these potassium channels that are regulating this process, either helping it return to its normal resting state, is making sure that the positive charges never get too intense, so that we have an appropriate response. And then, making sure that this returns to normal before it starts its next one. And you can see that these action potentials, they travel all the way down until they trigger the next neuron. So, that's how it happens. It starts in our brain, we're triggering, these neurons, and it travels from neuron to neuron, these positive charges, all the way till it gets to your hand, and that triggers it says, Hey, there's a big positive charge here. There's an action potential. It triggers your muscles and your bones to move your hand off that stove. And so that is what an action potential is, and that's how it travels from the brain to your hand to tell you to move. So, get that's a little complicated. I will be going over the individual steps later if you're still a little confused, but hopefully, you get just the basics of how these positive charges are being sent from neuron to neuron, and that's called an action potential. And that is really that electrical impulse that tells that allows your brain to tell your hand to move, and along with many other movements and things that our brain tells our body to do. So with that, let's move on.

Neuronal Signaling Steps

So in this video, we're going to be talking about the 7 steps to neuronal signaling. So what happens when a neuron needs to signal? It happens in 7 steps. We're going to walk through each step. It's kind of detailed. Just stay with me. Cell signaling involves a lot of steps, and this is just another one. So, like I said, the signal propagation between neurons occurs in 7 steps. So the first step is the neuron itself receives some type of signal, which triggers the opening of these cation channels, and the cation channel that's opened in the first step are sodium channels. And, so, when the sodium channels open, what happens is sodium rushes into the cell, and when it does, it creates this sort of influx of positive charge. And when there's an influx of positive charge, we call that depolarization. And, so, when this positive charge just rushes in so quickly, what happens is that those sodium channels then become inactivated. And it happens within a millisecond. I mean, so fast that these channels open, sodium rush in, then they're closed. To prevent this axon from continually just, you know, signaling. It needs to be regulated a short pulse. So the first step is the sodium or receive some type of signal, sodium channels open, comes depolarize and, now, there is this positive charge sitting in the neuron. So this depolarization triggers more voltage-gated ion channels to open, and there can be a variety of different ion channels, calcium, potassium, whatever. And this causes the depolarization to continually travel down the axon. So the axon has all these different ion channels at different regions along the axon. So as soon as the first one's open, it triggers the opening of all of them, and it then just tumbles down the axon. So the third step that happens is voltage-gated potassium channels open. But, remember, this is the third step. So it's important here that these are delayed in opening. And so, because now they're delayed, there's this really high positive charge inside the cell. And so, when these channels open, the potassium is actually transported out of the cell instead of in the cell, and this helps restore the neuron to its resting state. So, it's delayed. So, the most of the positive charge has already left. It's already traveled down, so it's somewhere else. But there's still this positive charge left behind where it just was, so those potassium channels open, the potassium flows out, and returns that section of the neuron to its original state. And, eventually, this traveling wave of depolarization reaches the end of the axon and the nerve terminal. So, what you're going to see here in this example, these are going to be kind of the first four steps. So, the first thing you'll see is up here, we're looking at sodium channels, which start out as closed, and then open and sodium rushes into the cell. But then, because they're only stays open for a really short amount of time, so it then closes and resets for the next action potential. And so down here, you're looking at this graph of membrane potential. So this is going to be charged. Remember that more positive is going to be inside the cell side, and more negative is going to be more negative inside the cell. So, this is kind of over time. So, you, again, you have step 1, where the sodium channels open. Sodium enters, so then it becomes more positive. The calcium channels are delayed in opening, so it begins to leave. But, the sodium channels here are still open, so it eventually reaches some type of peak, but then it starts traveling down. The potassium is leaving the cell, so the membrane potential is becoming more negative now, and everything eventually resets itself for another action potential. So those are the first four steps. But, like I said, there were 7. So now where we are is we've had this action potential. It's traveled down the axon. Now it's at the nerve terminal. So what happens now? So this electrical signal at the nerve terminal is then converted into a chemical signal because the synaptic cleft, which is the region between the two cells, the presynaptic and postsynaptic cell, can't pass electrical signals. So they can't pass an electrical charge, so it has to turn into a chemical signal. So the chemical signal that it uses is called a neurotransmitter. And how this works is neurotransmitters are already sitting in vesicles near the nerve terminal plasma membrane, so they're already just sitting there waiting for a signal to release them. So, when the depolarization or this positive charge arrives, it triggers, again, more voltage-gated calcium channels, and influx of calcium causes the vesicles to fuse with the plasma membrane and release the neurotransmitters into the synaptic cleft. So the neurotransmitters then are in the synaptic cleft, and they bind to receptors on the postsynaptic cell. Then this triggers the cell to fire action potentials and the cycle is repeated. But what happens to the neurotransmitter? Because now you have the signal, this chemical signal out there, and it doesn't need to continually be out there. Something needs to get rid of it. So, it needs to be removed and it is done through one of two methods. First, is the postsynaptic cell can destroy it, so it gets, sort of, uptake or taken in and destroyed, or it's released and, sort of, pumped back out and the presynaptic takes it up and reuses it. So that's how the neurotransmitter is released. So if we're watching this, what we get is we have our action potential arrives, and you have your neurotransmitters already sitting in these vesicles ready to fuse. So when the action potential gets here, that triggers the neurotransmitter or the vesicle fusion, which gets released into the synaptic cleft. And, when it does this, we'll move down here now. So now the neurotransmitters are in the synaptic cleft, so then they can bind to various, receptors on the postsynaptic cell. Receptors on the postsynaptic cell and trigger more action potential signaling further away. And remember, the neurotransmitters are destroyed either by the postsynaptic cell or they are recycled, again, pumped out and back into the presynaptic cell to be reused. So, those are the 7 steps to neuronal signaling. Feel free to review those steps again. Hopefully, I made it very clear. So with that, let's now move on.

Neurotransmitters

So in this video, we're going to talk more about neurotransmitters and specifically neurotransmitter signaling. Neurons must be able to interpret complex combinations of neurotransmitters. There's a bunch of different neurotransmitters, and they fall into two classes, excitatory or inhibitory. Excitatory neurotransmitters trigger an action potential in a postsynaptic cell, and that action potential then goes on to trigger more action potentials. An example of an excitatory neurotransmitter is acetylcholine, which is found in neuromuscular junctions and will actually induce action potentials resulting in muscle contraction.

The other class is the inhibitory neurotransmitter. Usually, what happens is inhibitory neurotransmitters trigger chloride channels to open, resulting in an influx of negative charge which makes depolarization harder. It reduces the impact of the action potential by helping to either decrease the intensity or reduce the chance of an action potential occurring. An example of an inhibitory neurotransmitter you might see is called GABA.

Some toxins and drugs work by targeting neurotransmitters. Here we have our excitatory and inhibitory. You have an excitatory neuron that's passing some type of exciting neurotransmitter, resulting in an action potential, which you can see because there is this peak of membrane potential. But an inhibitory one is going to have other types of neurotransmitters, resulting in a more negative charge which makes depolarization harder.

In this single cell receiving both excitatory and inhibitory neurotransmitters, what does it do? Well, there are these kinds of huge neuronal networks that receive large combinations of neurotransmitters. These are combinations of both excitatory and inhibitory signals, and each neuron contains its own set of receptors and ion channels, which can respond differently to all these different neurotransmitters. Neurons have to be able to combine and interpret all these signals, and you can imagine that it's hard for us to determine how the neuron is actually responding to all of these different combinations of signals, but it does. And it's what allows us to do the things that we do.

Now, when we talk about this, there is one term that I want to mention, and that's synaptic plasticity. And what that means is that the magnitude of a neuron's response depends on how much it has been used in the past. So a neuron that has been used or has received the same neurotransmitter a ton in the past is going to respond differently than a neuron that just receives it for the first time. I think the best analogy to this is smell. So if you walk into a room and there's this overwhelming smell of trash, that magnitude is you smell that smell and it is intense. Whereas, if you've been in that room for a couple of hours, you lose that sensitivity. The same things happen with neurons, but it's called synaptic plasticity.

This is just an example of neurons or a network, with different types of neurotransmitters. So you have some excitatory, some inhibitory, and this postsynaptic cell is going to take all this information and respond appropriately for whatever condition it's being stimulated for. So that's neurotransmitter signaling. Let's now move on.

Match the following neuron structure with its definition 

i. Cell Body                  ____________ 

ii. Myelin Sheath         ____________ 

iii. Nerve Terminal       ____________ 

iv. Nodes of Ranvier   ____________ 

v. Synapse                   ____________ 

a. Junction through which the signal is transmitted 

b. End of the axon that branches to pass the neurons message to many cells 

c. Core of the neuron 

d. Insulates the axon so ions do not leak out of the membrane 

e. Patches of ion channels that interrupt the sheath for neuron signaling

So this question is a matching question, and it says match the following neuron structure with its definition. So the first thing is a cell body. So what is a cell body? Well, if we look at these answers, is it a junction through which the signal is transmitted, the end of the axon that branches to pass the neuron's message to many cells? So the core of the neuron, that sounds very likely, so we'll put a mark next here. Does it insulate the axon? No. It doesn't. And does it is it a patch of ion channels? No. It's not. So the correct answer to cell body is going to be C. Now that we've read the answers, we might be able to go through the next ones a little bit faster. So myelin sheath, what does a myelin sheath do? Do you remember? Right. So that's responsible for insulating the axon. So we look at our answers, that's going to be D. Insulating the axons so ions do not leak out of the membrane. Now the third one says the nerve terminal. What does the nerve terminal do? Well, the nerve terminal is going to be the end of the axon that transmits signal. So if we look at our answers that most closely relates to B, which is the end of the axon that branches to pass, the neuron message to many cells, B. The 4th one is nodes of Ramvir. And, so, if you remember those are going to be groups or patches of ion channels. And so if we look at our answers that's going to be E. And, then we're left with the only one answer, the synapse, which has to then be A, which is the junction through which the signal is transmitted. So those, so that's a good review of neuron structures. Let's now move on.

What neuron structure is responsible for ensuring that ions do not leak out of the axon membrane?

• A. Cell body
• B. Dendrites
• C. Myelin sheath
• D. Nodes of Ranvier

The opening of which type of channel causes depolarization of the neuron?

• A. Voltage gated K⁺ channels
• B. Voltage gated Na²⁺ channels
• C. Voltage gated Ca²⁺ channels
• D. K⁺ leak channels

An influx of calcium at the synapse causes what to happen?

• A. Neurotransmitter release
• B. Neurotransmitter binding
• C. Depolarization
• D. Opening of the voltage gated K+ channels

Which of the following neurotransmitter types blocks Cl- channels and makes depolarization harder?

• A. Excitatory
• B. Inhibitory

Potassium channels are mainly responsible for what?

• A. Mediating action potentials
• B. Returning the neuron to a resting membrane potential
• C. Releasing neurotransmitters
• D. Depolarization

Here’s what students ask on this topic:

What is the structure and function of a neuron?

Neurons are specialized nerve cells that receive, integrate, and transmit signals. They have several key structures: the cell body (soma), which contains the nucleus; dendrites, which are short branches that receive signals; the axon, a long extension that conducts electrical signals away from the cell body; and the nerve terminal, which transmits signals to other cells. The axon is often covered by a myelin sheath, made by glial cells, which insulates the axon and speeds up signal transmission. Nodes of Ranvier, gaps in the myelin sheath, contain ion channels that facilitate rapid signal propagation. The synapse is the junction between neurons where signals are transmitted chemically via neurotransmitters.

How do action potentials work in neurons?

Action potentials are rapid electrical impulses that transmit signals along neurons. They begin when a neuron receives a stimulus, causing voltage-gated sodium channels to open and sodium ions to rush in, depolarizing the cell. This depolarization triggers adjacent sodium channels to open, propagating the signal down the axon. At the nerve terminal, the electrical signal converts to a chemical signal via neurotransmitters, which cross the synaptic cleft and bind to receptors on the postsynaptic cell, initiating a new action potential. Potassium channels then open to repolarize the cell, restoring the resting membrane potential.

What are the different types of neurotransmitters and their functions?

Neurotransmitters are chemical messengers that transmit signals across synapses. They can be excitatory or inhibitory. Excitatory neurotransmitters, like acetylcholine, trigger action potentials in postsynaptic cells, leading to responses such as muscle contraction. Inhibitory neurotransmitters, like GABA, open chloride channels, causing an influx of negative charge that makes depolarization harder, thus reducing the likelihood of an action potential. Neurons interpret complex combinations of these neurotransmitters to regulate various physiological processes and responses.

What is synaptic plasticity and why is it important?

Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time, based on their activity levels. This adaptability is crucial for learning, memory, and overall neural function. For example, a neuron that frequently receives a specific neurotransmitter will respond more robustly over time, enhancing signal transmission. Conversely, a neuron that rarely receives a neurotransmitter will have a diminished response. Synaptic plasticity allows the nervous system to adapt to new information and experiences, making it fundamental to cognitive processes.

How do voltage-gated ion channels contribute to action potentials?

Voltage-gated ion channels are essential for generating and propagating action potentials. When a neuron is stimulated, voltage-gated sodium channels open, allowing Na⁺ ions to enter the cell, causing depolarization. This depolarization triggers adjacent sodium channels to open, propagating the action potential along the axon. To repolarize the cell, voltage-gated potassium channels open, allowing K⁺ ions to exit, restoring the negative resting membrane potential. These channels ensure the rapid and unidirectional transmission of electrical signals in neurons.