Neuron & Action Potential Simulator
Stimulate a neuron and watch it fire (or fail to fire) an action potential, with a live resting → threshold → depolarization → repolarization → hyperpolarization voltage graph.
Set the stimulus and channel conductances, then press Stimulate. Watch the impulse race down the axon and read the voltage trace: resting → threshold → depolarization → repolarization → hyperpolarization.
About the Neuron & Action Potential Simulator
Free neuron & action potential simulator. Stimulate a neuron and watch it fire (or fail to fire) an action potential, with a live resting → threshold → depolarization → repolarization → hyperpolarization voltage graph. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for biology, the neuron & action potential simulator runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Stimulate a neuron and watch it fire (or fail to fire) an action potential, with a live resting → threshold → depolarization → repolarization → hyperpolarization voltage graph. Use it to explore biology ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Neuron & Action Potential Simulator
- Use the controls to change Resting potential, Sodium (Na⁺) conductance, Potassium (K⁺) conductance, Stimulus strength, Myelination. The simulation reacts instantly.
- Pick an option such as Myelinated, Unmyelinated to switch modes or load an example.
- Press "Stimulate", "Check my stimulus", "Check both conditions", "Reset to defaults" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Set the stimulus just below threshold and watch the graded potential fade without firing.
- Switch off myelination and compare how long the impulse takes to reach the terminal.
- Raise potassium conductance and watch the hyperpolarization deepen.
- Find the smallest stimulus that still produces a full-size spike.
Key ideas you can learn
- An action potential only fires once the stimulus reaches threshold - the all-or-none law.
- Depolarization is caused by sodium (Na⁺) rushing in; repolarization by potassium (K⁺) rushing out.
- A myelinated axon conducts much faster because the signal jumps between nodes of Ranvier (saltatory conduction).
- Below threshold, only a small graded potential occurs and fades away.
Where this is used in the real world
This is exactly how doctors interpret nerve conduction studies, and why multiple sclerosis (which damages myelin) slows and sometimes blocks nerve signals.
Who is this simulation for?
Biology students and teachers who want to explore living systems, populations and genetics interactively and safely.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
What is the all-or-none law?
Once a stimulus reaches threshold, the action potential always fires at full size; stronger stimuli do not make a bigger spike, only more frequent ones.
Why is myelinated conduction so much faster?
The signal skips along by jumping from one node of Ranvier to the next instead of regenerating continuously along the whole membrane.
Is the Neuron & Action Potential Simulator free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Neuron & Action Potential Simulator work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.