The Action Potential
Lesson notes
Overview
A nerve cell fires an all-or-none electrical spike once its stimulus passes a threshold. This topic is rated intermediate and is number 32 of 110 in Biology. Builds on the basics with relationships, methods and trade-offs.
What you are seeing
The panel above shows a living system animated over time. 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
A nerve cell at rest has an electrical potential of about −70 mV across its membrane. If a stimulus pushes it above a threshold, voltage-gated sodium channels open, sodium rushes in and the potential jumps to about +40 mV; then potassium channels open and the potential returns. The all-or-none spike moves along the axon at speeds of up to 100 m/s, faster in myelinated fibres where it jumps between gaps. A stronger stimulus makes more frequent spikes, not larger ones.
Reading the relationship
The expression "V_m rises from −70 mV" is a compact summary of the idea. It uses the symbols V_m, r, i, s, e, f; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.
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 “Temperature and Enzyme Activity”, the topic before it in Biology. Once you are comfortable, continue with “The Synapse”.
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 “The Action Potential” 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 The Action Potential?
A nerve cell fires an all-or-none electrical spike once its stimulus passes a threshold. It is an intermediate topic in Biology.
How do I use the The Action Potential simulation?
The panel at the top shows a living system animated over time. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression V_m rises from −70 mV 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?
Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Temperature and Enzyme Activity”, 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.