Click image to open full size
Biology
Grade 11-12
Neuron Action Potential Reference Cheat Sheet
A printable reference covering resting potential, threshold, depolarization, repolarization, refractory periods, ion channels, and action potential graphs for grades 11-12.
Related Tools
Related Labs
Related Worksheets
This cheat sheet covers how neurons generate and transmit action potentials, the rapid electrical signals used for communication in the nervous system. Students need this reference to connect membrane voltage changes with ion movement, channel behavior, and signal direction. It is especially useful for reading action potential graphs and understanding how neurons encode information. The focus is on clear stages, key voltages, and the roles of sodium and potassium ions.
Key Facts
- A typical resting membrane potential is about -70 mV, with the inside of the neuron more negative than the outside.
- Threshold is usually about -55 mV, and reaching it triggers an all-or-none action potential.
- Depolarization occurs when voltage-gated Na+ channels open and Na+ rushes into the neuron, making the membrane potential more positive.
- Repolarization occurs when voltage-gated Na+ channels inactivate and voltage-gated K+ channels open, allowing K+ to leave the neuron.
- Hyperpolarization occurs when K+ channels close slowly, causing the membrane potential to briefly become more negative than resting potential.
- The sodium-potassium pump helps maintain ion gradients by moving 3 Na+ out of the cell and 2 K+ into the cell using ATP.
- The absolute refractory period prevents a second action potential because voltage-gated Na+ channels are inactivated.
- Action potentials travel in one direction along an axon because the membrane behind the signal is temporarily refractory.
Vocabulary
- Resting membrane potential
- The voltage across a neuron's membrane when it is not sending an action potential, usually about -70 mV.
- Threshold
- The membrane voltage, usually about -55 mV, that must be reached to trigger an action potential.
- Depolarization
- The stage of an action potential when the inside of the neuron becomes more positive due to Na+ entering the cell.
- Repolarization
- The stage when the membrane potential becomes more negative again as K+ leaves the cell.
- Refractory period
- The short recovery time after an action potential when the neuron cannot fire or is harder to fire.
- Myelin sheath
- An insulating layer around some axons that speeds signal conduction by allowing impulses to jump between nodes.
Common Mistakes to Avoid
- Confusing depolarization with repolarization is wrong because depolarization is caused mainly by Na+ entering, while repolarization is caused mainly by K+ leaving.
- Thinking a stronger stimulus makes a larger action potential is wrong because action potentials are all-or-none and do not increase in height after threshold is reached.
- Ignoring the refractory period is wrong because it explains why action potentials travel forward and why neurons need time before firing again.
- Saying the sodium-potassium pump directly causes the spike is wrong because the spike is mainly produced by voltage-gated ion channels, while the pump maintains long-term ion gradients.
- Reading voltage values without signs is wrong because -70 mV and +30 mV represent very different membrane states and ion movements.
Practice Questions
- 1 A neuron has a resting potential of -70 mV and threshold of -55 mV. How many millivolts must the membrane potential increase to reach threshold?
- 2 During an action potential, the membrane voltage rises from -55 mV to +30 mV. What is the total change in membrane potential?
- 3 If one sodium-potassium pump cycle moves 3 Na+ out and 2 K+ in, how many Na+ ions move out after 10 cycles?
- 4 Explain why an action potential usually travels in only one direction along an axon.