Nernst Potential for Potassium
Lesson notes
Overview
The equilibrium potential depends on the ratio of ion concentrations. This topic is rated advanced and is number 85 of 110 in Biology. Deeper models, formal results and harder reasoning.
What you are seeing
The panel above shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
The equilibrium potential of an ion is the membrane voltage at which the electrical force balances the diffusion due to the concentration difference: E = (RT/zF) ln([out]/[in]). For potassium, with about 5 mM outside and 140 mM inside, it is about −90 mV, near a nerve cell’s resting potential, which is why the membrane is mostly permeable to K⁺ at rest. For sodium it is about +60 mV, which drives the upstroke of the action potential.
Reading the relationship
The expression "E = (RT/zF) ln([out]/[in])" is a compact summary of the idea. It uses the symbols E, R, T, z, F, o; name what each one stands for before you start. Notice that it contains a ratio, so increasing the denominator makes the result smaller, and a logarithm, which turns multiplication into addition and compresses large values. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Set every slider to its middle value and note the shape of the curve. 2. Move one slider at a time and describe whether the curve shifts, stretches or turns. 3. Find the value where the behaviour changes sharply, then connect it to the formula.
Try this
Try to explain why the pattern holds, not just what it is. Look for limiting cases and what happens at the edges.
Common pitfalls
Biological processes are rarely all-or-nothing. Look for the feedback, the timing and the exceptions, rather than learning a single fixed sequence by heart.
How it connects
It builds on “Hodgkin–Huxley Sodium Gate Idea”, the topic before it in Biology. Once you are comfortable, continue with “Reaction Time and Distance”.
Why it matters
Biology shows how living things are built and how they work, grow, inherit traits and adapt.
Where you might use it
- Revising “Nernst Potential for Potassium” before a class, exam or certification
- Understanding inherited conditions, medicines and how the body responds to disease
- Working in farming, conservation and food production, where populations and genes matter
- Following news about vaccines, genetic testing and climate effects on wildlife
Frequently asked questions
What is Nernst Potential for Potassium?
The equilibrium potential depends on the ratio of ion concentrations. It is an advanced topic in Biology.
How do I use the Nernst Potential for Potassium simulation?
The panel at the top shows a graph of the function. Each slider changes one parameter, so you can see exactly how the curve bends, shifts or stretches. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression E = (RT/zF) ln([out]/[in]) packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Deeper models, formal results and harder reasoning. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Hodgkin–Huxley Sodium Gate Idea”, the previous topic in Biology. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.