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.
Vm -70 mVThreshold -55 mVSpikes 0
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?