Neuron Action Potential Simulator
Trigger an electrical stimulus on a neuron and watch the membrane potential graph trace typical Depolarization, Repolarization, and Hyperpolarization phases. Track the live states of Na+ and K+ ion channels.
HOW NERVE CELLS FIRE
An **action potential** is a rapid, electrical signal that travels along the axon of a neuron. It is an 'all-or-nothing' event, meaning the signal either fires at full strength or not at all. This process is the fundamental mechanism of communication in the nervous system.
STAGES OF THE ACTION POTENTIAL
1. **Resting Potential**: The cell is at -70mV, maintained by the Na+/K+ pump. 2. **Depolarization**: A stimulus triggers voltage-gated **Sodium () channels** to open. rushes in, making the inside positive (+30mV). 3. **Repolarization**: channels close and voltage-gated **Potassium () channels** open. rushes out, bringing the voltage back down. 4. **Hyperpolarization**: The channels stay open slightly too long, causing the voltage to dip below the resting state (the refractory period).
HOW TO USE THIS VISUALIZATION
1. **Stimulate the Axon**: Click to trigger a signal. Watch the voltage graph jump. 2. **Watch the Channels**: Observe the colored gates as they open and close in sequence. 3. **Monitor Ion Flow**: Follow the (blue) and (red) ions as they move through the membrane. **Try This**: Repeatedly stimulate the cell. Notice how you cannot fire a second action potential while the first one is finishing. This is the **refractory period**. Why is this period necessary for one-way signal propagation?
AP EXAM CONNECTION
Unit: Unit 4: Cell Communication and Cell Cycle (Topic 4.3)
Learning Objective: IST-3.E
COMMON MISCONCEPTIONS
- Thinking the action potential travels as a 'flow' of electrons (it is a wave of ion movement).
- Believing sodium and potassium swap places permanently (the pump restores them).
- Confusing the resting potential with the action potential.
KEY TAKEAWAYS
- Action potentials are all-or-nothing.
- Sodium in = Depolarization.
- Potassium out = Repolarization.
- Refractory periods ensure one-way flow.
PRACTICE QUESTIONS
Q1 (CONCEPTUAL): What event triggers the rapid depolarization phase of the action potential?
Show Answer & Explanation
Answer: Opening of voltage-gated sodium channels.
Explanation: Once the threshold voltage is reached, sodium channels open quickly, allowing positive ions to flood into the cell.
Q2 (CONCEPTUAL): Which ion is responsible for returning the neuron to a negative potential during repolarization?
Show Answer & Explanation
Answer: Potassium (K+).
Explanation: Potassium ions exit the cell, removing positive charge and restoring the internal negative voltage.
