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### Course: NCLEX-RN>Unit 16

Lesson 2: Neuron membrane potentials

# Neuron resting potential mechanism

This video explores the creation of neuron resting potential and its relation to ion concentration differences. It highlights the role of organic anions, sodium potassium pump, and leak channels. The concept of equilibrium potential is explained, along with the impact of ion concentrations on neuron function. Created by Matthew Barry Jensen.

## Want to join the conversation?

• somehow I feel like I knew more about resting potential prior to seeing this video. The presenter seems very intelligent but it might be good if he could highlight the key takeaways. He presents a lot of information and it's not clear what MCAT org wants the audience to perceive as important
• Very true. If the video isn't clear in its presentation, the information will still be hard to understand, no matter how simple it is in reality.
• Why is -60mV given as the resting membrane potential when A&P textbooks give it as -70mV?
• My textbook lists it as 56mV, so it just depends on what you are reading, and what they think is a typical value for it, in reality it differs based on the type if neuron you are studying.
• Making organic anions inside the cell cannot create a membrane potential; this violates conservation of charge. The pump adds only 2-3 mV, not 5. Since 2/3 of body water is inside cells, the outside ion concentrations do not remain constant via dilution, but rather through homeostatic control, e.g. via kidney. Pump does not create concentration gradients, cells arrive by fission, so they get them at birth. As you point out, pumps are to maintain the gradients, but do not create them. You might as well use the proper equilibrium potentials, e.g. in a neuron Ek is -90, not -70mV. And resting Vm is usually said to be -70 mV. The ratio of resting permeabilities is 40:1, not 25 to 1.
My suggestions are based on numbers from awhile ago, which might have changed, if so, I apologize. On the whole, this video goes through equilibium and then resting membrane potentials all at once, and quickly. When I teach, I break them up as the concepts often seem counterintuitive. Steve Eiger
• None of the complex statements you've made are relevant as so for as a Neuroscientist or Neurophysiologist is concerned. Bringing kinetic theory into the picture is more likely to confuse the topic than to clarify it.
• At we are told that the diffusion force will be forcing the K+ out to a lower concentration. However at we are told that the extracellular fluid is huge and total number of ions in it is huge. Wouldn't this mean that the concentration gradient would always be out to in? I know it isn't but I can't get my head round this point. Thanks
• You are mixing up amount and concentration.
Inside the cell there is a high concentration of K+, so it would like to escape. But the volume of a cell is very very small.

The outside on the other hand is very very big. so it naturally contain more K+. But the concentration is low. And osmosis follows concentration difference, not amount.

Just like i can make a bottle of salt water with 10% salt.
If i put it in the ocean, with a low 3.5% salt, the diffusion will make the salt leave the bottle. Even though the ocean volume is huge and have much more salt.

I hope yo understand.
• How does the potassium/chloride simporter work if potassium has already equilibrated?
• The K+/Cl- symporter will only work if there is a K+ gradient. It relies on the force from this concentration gradient to operate.
• AT , does that mean that at -120mV, Ca2+ will get pumped outward the neuron?
• Well, what the guy basically says it is that the concentration inside the neuron of Ca2+ is usually low when it gets pumped out of the neuron with the Ca2+./Na+ pump so if you want a big concentration of Ca2+ inside of the neuron you need to pump as much calcium IN in order to reach (POSITIVE) +120mV. At that value you can say you have enough Ca2+ inside the neuron.
• Do the chloride-potassium symporter and the sodium-calcium exchanger require ATP too? I was thinking about the word symporter so I assumed that has somtething to do with symport? Is that correct?
• You are on the right track; a symporter moves two different molecules in the same direction. However, this mechanism does not require ATP, because one of the participating ions (potassium in the first case and sodium in the second case) is flowing down its gradient, a process that does not require energy input. This action is what powers the transfer of the other ion against its gradient. :)