Which part of the living system did you change?
Labs / Biology
Action Potential
Press Stimulate (or click the trace) to inject a jolt of current into a neuron. A weak nudge just makes the voltage bump and fade, but push past the −55 mV threshold and the membrane fires a full spike — a fast rise to +40 mV, a sharp fall, and a brief refractory pause before it can fire again.
Labs / Biology / Action Potential
Action Potential
Press Stimulate (or click the trace) to inject a jolt of current into a neuron. A weak nudge just makes the voltage bump and fade, but push past the −55 mV threshold and the membrane fires a full spike — a fast rise to +40 mV, a sharp fall, and a brief refractory pause before it can fire again.
Why it matters
Why explore this?
Living systems are connected and constantly changing. This model makes one biological process visible so you can test how its parts affect one another.
Explore
Try the model
Vm -70 mVThreshold -55 mVSpikes 0
Investigate
Questions to test
Predict first, try it in the model, then use what you observe to answer.
What to try
- Slide the stimulus down to “Sub-threshold.” Why does the voltage twitch and then give up instead of spiking?
- What is the smallest stimulus that still fires a spike — and once it fires, does a stronger jolt make the spike any taller?
- Turn on Auto-fire. Why can't the neuron simply fire faster and faster as you crank up the strength?
- Watch the dip below the resting line after each spike. Would it be easier or harder to fire a second spike right then?
- The amber ticks along the bottom mark when current is flowing. How much does the voltage lag behind the moment you stimulate?
Explain
Make sense of what happened
Explain the process as a chain: a change happens, the system responds, and that response affects what happens next. Use an observation from the model as evidence.
Check
Before you leave
How did the system respond?
How would you explain that response?
If you can answer all three using evidence from the model, you understand the main idea. If not, return to Explore and change one setting at a time.