Resting Membrane Potential - Online Tutor, Practice Problems & Exam Prep

Resting membrane potential is the voltage difference across a cell membrane when the cell is not stimulated, typically around -70 millivolts in the CNS. This potential arises from the unequal distribution of ions, primarily sodium (Na⁺) outside and potassium (K⁺) inside the cell, along with the cell's permeability to these ions. The sodium-potassium pump maintains these gradients by ejecting 3 Na⁺ ions and bringing in 2 K⁺ ions, stabilizing the resting potential crucial for neuronal communication.

Resting Membrane Potential

Alright. So this video is about resting membrane potential. As you may recall from earlier in the chapter, membrane potential is the voltage created from charge separation between the interior and exterior of the cell. When I say charge separation, I literally mean that the inside and outside of the cell have different charges. For example, one could be positive and the other could be negative.

That difference in charge creates electrical potential. That's what we're dealing with here. Resting potential is the membrane potential of a cell that is not being stimulated. The neuron is literally resting; it's just not doing anything.

Typical resting potential in the CNS is approximately negative 70 millivolts. There is a range here; it can be from between negative 40 to negative 90 millivolts depending on the type of neuron and its location in the human body. Do keep that in mind, but for most neurons in the CNS, negative 70 is a pretty normal resting potential. We're going to use that in all our examples going forward, just so you know. Another way to articulate this is that when a cell is at rest, the interior of the cell is more negative than the exterior.

Resting potential is created by two factors. The first factor is the differences in ionic composition of the intracellular and extracellular fluid. This might sound a bit complex, but you actually already know this. Recall, when a cell is at rest, we see more sodium outside the cell and more potassium inside the cell.

These concentrations of sodium and potassium are a significant factor in creating resting potential. The other major factor here are the differences in plasma membrane permeability to those ions. As you may recall from when we first introduced ion channels, neurons have a lot more leak channels for potassium than for sodium. This means that our neuron is more permeable to potassium than to sodium. These two factors combined mean that we have a lot of sodium outside the cell, so its concentration gradient wants it to go into the cell. And we have a lot of potassium inside the cell, which means its concentration gradient is going to direct it out of the cell.

Because the cell is so permeable to potassium, a lot of potassium can leak out of the cell. Because we have so many positive potassium ions leaking out, that creates this negative cell interior. Potassium ions are kind of like the MVPs of resting potential. Sodium is playing its part, it's doing its job, but potassium is really the big factor here. So, that is how our resting potential has been created. And now that we have it, it's going to be stabilized by our trusty sodium-potassium pump, which is going to maintain those concentration gradients for sodium and potassium.

It does that, remember, by constantly ejecting 3 sodium ions while pulling back 2 potassium ions to help maintain that concentration of potassium inside the cell. That is resting potential in a nutshell. What I just covered so far is what most standard anatomy and physiology courses will want you to know about resting potential. If you feel like you have a good handle on this, please feel free to stop the video right now.

If you're feeling unsure or if you have some questions, stick around for a few minutes because I'm going to go over some common questions students have about resting potential. So, the first very common question I get is, if there are so many positively charged potassium ions inside the cell, why is the cell negative? Which is a very intuitive and excellent question.

It's important to remember that while we are focusing on the roles of sodium and potassium here, there are other things happening. There are other types of ions, some of them negatively charged, and very importantly, there are lots of negatively charged proteins inside the cytosol. So, potassium and sodium play a big role in creating resting potential but they are not the only factors contributing to that negative cell interior.

Another question I often get is, why are we letting so much potassium leak out of the cell? Why do we have so many leak channels, if our poor pump is working so hard to bring it back in all the time? This is also a great question. Potassium leak channels play a significant role in creating resting potential, but they also have other functions. Recent research has implicated them in roles such as pain signaling, sleep duration, and potentially even movement. So, those leak channels have additional functions aside from just creating resting potential.

The last question I often get is, if we want the interior of the cell to be negative, why is our sodium-potassium pump bringing in positively charged ions? Isn't that counterintuitive? Remember, the role of the pump is to maintain the concentration gradient. By stabilizing the concentrations, it stabilizes the concentration gradients, thereby stabilizing the rate of diffusion. If our pump were to stop working, the rate of diffusion would become unstable, which could result in too much potassium leaking out of the cell, making our cell excessively negative.

We aim to maintain that negative 70 millivolts, our “Goldilocks zone,” where everything is just right. Hopefully, that helped clear some things up for you. If you have other questions, please feel free to leave them in the comments, and we'll try to get back to you as quickly as we can. I'll see you guys in the next video. Bye bye.

Resting Membrane Potential Example 1

Okay. So let's jump into an example here. Our question reads, which of the following is the most accurate regarding the sodium potassium pump? Alright. Option A has, the sodium potassium pump creates resting potential by ejecting 3 potassium ions and transporting 2 sodium ions into the cell.

And, whew, that's a doozy of incorrect information. Right? The sodium potassium pump does not create resting potential. No, no. It stabilizes it.

And we are ejecting 3 sodium ions, so this is wrong. And we should be transporting 2 potassium ions, so this is also wrong. So A is out. Right? Option B reads, the sodium potassium pump is the main factor in creating resting potential.

Now it's that same word again, creating. It does not create it. It stabilizes it. So B is out. Option C reads, the sodium potassium pump directly impacts resting potential by allowing more negatively charged ions into the cell.

Now we know that the sodium potassium pump works with sodium and potassium, both of which are positively charged ions. So C is out, so it's probably D, but let's just read it. The sodium potassium pump stabilizes, there's that word, resting potential in a neuron, and that is absolutely correct, so our answer is D. And there you go.

Which of the following is the MOST important factor in generating resting membrane potential?

• A. Na+ concentration gradient.
• B. K+ concentration gradient.
• C. K+ electrical gradient.
• D. Na+/K+ ATPase.

Here’s what students ask on this topic:

What is resting membrane potential and why is it important?

Resting membrane potential is the voltage difference across a cell membrane when the cell is not stimulated, typically around -70 millivolts in the central nervous system (CNS). This potential is crucial because it sets the stage for action potentials, which are essential for neuronal communication. The resting membrane potential arises from the unequal distribution of ions, primarily sodium (Na⁺) outside and potassium (K⁺) inside the cell, along with the cell's permeability to these ions. The sodium-potassium pump maintains these gradients by ejecting 3 Na⁺ ions and bringing in 2 K⁺ ions, stabilizing the resting potential. This balance is vital for the proper functioning of neurons and muscle cells.

How is the resting membrane potential established?

The resting membrane potential is established by two main factors: the differences in ionic composition of the intracellular and extracellular fluids, and the differences in plasma membrane permeability to these ions. There is more sodium (Na⁺) outside the cell and more potassium (K⁺) inside the cell. The cell membrane is more permeable to K⁺ due to more potassium leak channels, allowing K⁺ to exit the cell, making the interior more negative. The sodium-potassium pump helps maintain these gradients by ejecting 3 Na⁺ ions and bringing in 2 K⁺ ions, stabilizing the resting potential around -70 millivolts.

Why is the interior of the cell negative if there are positively charged potassium ions inside?

Even though there are positively charged potassium (K⁺) ions inside the cell, the interior remains negative due to several factors. First, the cell membrane is more permeable to K⁺, allowing these ions to leak out, which contributes to a negative charge inside. Additionally, there are negatively charged proteins and other ions within the cytosol that contribute to the negative charge. The combined effect of these factors results in a net negative charge inside the cell, despite the presence of K⁺ ions.

What role does the sodium-potassium pump play in maintaining the resting membrane potential?

The sodium-potassium pump is crucial for maintaining the resting membrane potential. It actively transports 3 sodium (Na⁺) ions out of the cell and 2 potassium (K⁺) ions into the cell, using ATP for energy. This action maintains the concentration gradients of Na⁺ and K⁺, with more Na⁺ outside and more K⁺ inside the cell. By stabilizing these gradients, the pump ensures that the resting membrane potential remains around -70 millivolts, which is essential for the proper functioning of neurons and muscle cells.

Why are there more potassium leak channels than sodium leak channels in the cell membrane?

There are more potassium (K⁺) leak channels than sodium (Na⁺) leak channels in the cell membrane because potassium plays a more significant role in establishing the resting membrane potential. The higher number of K⁺ leak channels allows more K⁺ to exit the cell, contributing to the negative charge inside. This differential permeability is crucial for maintaining the resting membrane potential around -70 millivolts. Additionally, recent research suggests that potassium leak channels may also be involved in other physiological processes such as pain signaling, sleep duration, and movement.