Action Potential Graph Maker
Generate labeled action potential graphs of resting potential, threshold, depolarization, repolarization and hyperpolarization with the Na⁺ and K⁺ channel events, for neuron, cardiac and muscle cells. Written for physiology.
Action potential graph examples
Real renders of the prompts shown: a fully labeled neuron action potential, a five-label school version, a cardiac action potential with phases 0–4 and a blank worksheet. Click one to load and edit its prompt.
Labeled action potential graph: one spike from stimulus to rest
Read the curve left to right: membrane potential in millivolts up the side, time in milliseconds along the bottom, threshold and rest as the two dashed lines.
- 1
Stimulus → threshold (−55 mV)
At 1 ms a stimulus lifts the membrane from rest at −70 mV to threshold.
- 2
Depolarization → peak (+30 mV)
Voltage-gated Na⁺ channels open and Na⁺ rushes in; the curve passes 0 mV in well under a millisecond.
- 3
Repolarization
Na⁺ channels inactivate, voltage-gated K⁺ channels open, K⁺ flows out and the curve falls.
- 4
Undershoot → rest
K⁺ keeps leaving, so the curve dips below −70 mV before settling back at rest near 4 ms.
Neuron, heart, muscle: action potential graphs and diagrams compared
The shape of the curve depends on the cell, and some figures show the membrane or the axon instead of a graph. Give the cell type and the values your course uses; these are the common versions.
Neuron action potential graph
The default above: rest at about −70 mV, threshold at about −55 mV, a peak near +30 mV, an undershoot toward the K⁺ equilibrium potential of about −90 mV, all within 2 to 4 ms. For a physiology course, add the Na⁺ and K⁺ conductance curves under the spike: Na⁺ conductance rises and falls within the upstroke, K⁺ conductance rises later and lasts into the undershoot.
Action potential diagram of the axon
A stretch of axon instead of a graph: at the active patch Na⁺ flows in and the inside turns positive, just behind it K⁺ flows out and the membrane is refractory, ahead of it the membrane is still at rest. Arrows of local current show why the impulse moves forward and not back. Ask for the voltage-gated Na⁺ channel drawn in its three states: closed, open, inactivated.
Cardiac action potential graph
A ventricular muscle cell, numbered phase 0 to phase 4: phase 4 rest at about −90 mV; phase 0 a fast upstroke through Na⁺ channels; phase 1 a small notch as transient K⁺ channels open; phase 2 a plateau near 0 mV while Ca²⁺ enters through L-type channels and balances K⁺ leaving; phase 3 repolarization as K⁺ channels take over. The whole curve lasts about 250 to 300 ms, so the time axis is in hundreds of milliseconds.
SA node action potential graph
The pacemaker curve, with no flat resting line. Phase 4 drifts upward from about −60 mV through the slow inward “funny” current and then T-type Ca²⁺ channels; at about −40 mV L-type Ca²⁺ channels open for a slow, rounded upstroke (phase 0) that peaks at about +15 mV; K⁺ channels bring it back down (phase 3). There are no phases 1 or 2. Draw several cycles in a row to show the automatic rhythm.
Skeletal muscle action potential graph
Short like a neuron’s, a few milliseconds, but starting from a resting potential of about −90 mV. It begins at the neuromuscular junction, where acetylcholine opens ligand-gated channels and the end-plate potential brings the fiber to threshold, then spreads along the sarcolemma and down the T-tubules. Draw it above the twitch it triggers, which lasts tens of milliseconds, to show which comes first.
Resting membrane potential diagram
The membrane before any spike: about 140 mM K⁺ inside against 4 to 5 mM outside, about 145 mM Na⁺ outside against 10 to 15 mM inside. K⁺ leak channels let K⁺ seep out and leave the inside negative; the Na⁺/K⁺ pump moves 3 Na⁺ out and 2 K⁺ in for each ATP and keeps the gradients in place.
Saltatory conduction diagram
A myelinated axon with the action potential jumping from one node of Ranvier to the next, the myelin between them insulating the axon so the current spreads quickly inside it. Label the speeds for contrast: up to about 120 m/s in large myelinated fibers, around 1 m/s in thin unmyelinated ones.
Graded potential graph
Small bumps of different sizes below the threshold line, for EPSPs, and dips below rest, for IPSPs. Show summation: one EPSP alone fades, two arriving close together add up past −55 mV and set off a full spike. This is the graph that explains why threshold matters.
Phases of the action potential: ion channels and membrane potential
The phases a labeled action potential graph is normally expected to show, the ion channel event behind each one, and where it sits on the voltage axis. This is the default label set unless you ask for a shorter one.
| Phase | What the ion channels do | Membrane potential |
|---|---|---|
| Resting potential | Voltage-gated channels are closed; K⁺ leak channels and the Na⁺/K⁺ pump hold the membrane steady | About −70 mV |
| Stimulus | A graded potential, for example from a synapse, lets positive charge in and depolarizes the membrane | From −70 mV toward −55 mV |
| Threshold | Enough voltage-gated Na⁺ channels open for the rise to become self-sustaining | About −55 mV |
| Depolarization (rising phase) | Voltage-gated Na⁺ channels open fully and Na⁺ rushes into the cell | From −55 mV up through 0 mV |
| Peak (overshoot) | Na⁺ channels inactivate as the slower voltage-gated K⁺ channels open | About +30 mV |
| Repolarization (falling phase) | K⁺ flows out through the open voltage-gated K⁺ channels | From the peak back down toward −70 mV |
| Hyperpolarization (undershoot) | The K⁺ channels close late, so K⁺ keeps leaving for a moment | Briefly below −70 mV |
| Return to resting potential | The K⁺ channels close; leak channels and the Na⁺/K⁺ pump restore rest | Back to about −70 mV |
| Absolute refractory period | Na⁺ channels are open or inactivated, so no stimulus can start a second spike | From threshold through the peak and most of the fall |
| Relative refractory period | Some Na⁺ channels have reset but K⁺ is still leaving, so only a stronger stimulus works | The end of the fall and the undershoot |
Courses differ in how many phases they name. Introductory worksheets label the resting potential, threshold, depolarization, repolarization and hyperpolarization; A-level, AP and university courses add the stimulus, the peak, the channel events and both refractory periods, and some textbooks put the peak at +40 mV rather than +30 mV. Name the labels and values you need and only those are drawn.
What is an action potential graph?
An action potential graph plots a neuron's membrane potential in millivolts against time in milliseconds: from a resting potential of about −70 mV the membrane depolarizes past a threshold of about −55 mV, spikes to about +30 mV, repolarizes, dips briefly below rest and returns to −70 mV. Each phase is labeled with the ion channels that drive it.
Key facts
- The whole spike lasts about 1 to 2 milliseconds in a neuron. The membrane potential swings about 100 mV, from −70 mV at rest to about +30 mV at the peak, and is back at rest a few milliseconds later.
- Voltage-gated Na⁺ channels drive depolarization. Once a stimulus brings the membrane to about −55 mV they open, Na⁺ rushes in and the rise feeds itself — a positive-feedback loop that makes the upstroke almost vertical.
- Voltage-gated K⁺ channels drive repolarization. They open more slowly than the Na⁺ channels, about when the Na⁺ channels inactivate at the peak, so K⁺ flows out and the membrane potential falls back.
- The undershoot comes from K⁺ channels that close late. Potassium keeps leaving for a moment after rest is reached, pulling the membrane below −70 mV toward the K⁺ equilibrium potential of about −90 mV before the Na⁺/K⁺ pump and leak channels restore rest.
- Action potentials are all-or-none. A stimulus that does not reach threshold produces no spike, and every stimulus that does produces the same spike to the same peak; a stronger stimulus fires more spikes per second, not bigger ones.
Graded potential vs action potential: what is the difference?
A graded potential is a small, local change in membrane potential whose size follows the strength of the stimulus and fades with distance; an action potential is an all-or-none spike to about +30 mV that fires only at threshold and travels the length of the axon without shrinking. Graded potentials on the dendrites and cell body add up at the start of the axon, and an action potential fires there only if their sum reaches threshold.
| Graded potential | Action potential | |
|---|---|---|
| Size | Varies with the strength of the stimulus | Always the same, about 100 mV from rest to peak (all-or-none) |
| Direction | Depolarizing or hyperpolarizing | Always depolarizes, then repolarizes |
| Threshold | None — any stimulus produces one | Fires only when the membrane reaches about −55 mV |
| Over distance | Fades within a short distance of where it starts | Regenerated along the axon at full strength |
| Where it happens | Dendrites, cell body and sensory receptors | The axon, from its initial segment to the axon terminals |
| Summation and refractory period | Can add together; no refractory period | Cannot add together; followed by a refractory period |
On a graph, a graded potential is a small bump that stays below the threshold line, or a dip below rest; an action potential is the tall spike that crosses threshold, overshoots 0 mV and undershoots rest. If a drawing shows spikes of different heights for different stimuli, it is showing graded potentials, not action potentials.
Common questions about action potential graphs
What are the 5 phases of an action potential?
Most courses name five: the resting potential, threshold, depolarization, repolarization and hyperpolarization (the undershoot), after which the membrane returns to rest. Some count the stimulus or the peak as a phase instead of threshold. On the graph they run in that order from left to right, all within about 2 ms in a neuron.
What should a labeled action potential graph include?
Membrane potential (mV) on the vertical axis and time (ms) on the horizontal axis, dashed lines for the resting potential (−70 mV) and threshold (−55 mV), and the stimulus, depolarization, peak (+30 mV), repolarization, hyperpolarization and return to rest on one spike. A&P and medical courses add the Na⁺ and K⁺ channel events and the absolute and relative refractory periods. That is the default — ask for fewer labels and only those are drawn.
What is the resting membrane potential?
The voltage across a neuron’s membrane when it is not firing, about −70 mV, inside negative to outside. It comes mainly from K⁺ leaking out through open leak channels, down a gradient of about 140 mM inside to 4 to 5 mM outside; the Na⁺/K⁺ pump, moving 3 Na⁺ out and 2 K⁺ in per ATP, keeps the gradients from running down. Heart and skeletal muscle cells rest nearer −90 mV.
Why does the membrane potential overshoot to +30 mV?
Because Na⁺ keeps flowing in after the inside of the membrane passes 0 mV, pushed by its steep concentration gradient. The membrane heads toward the Na⁺ equilibrium potential of about +60 mV, but the Na⁺ channels inactivate and the K⁺ channels open first, so the peak stops near +30 mV.
What is the refractory period?
The time after a spike when the membrane cannot fire again (absolute refractory period) or needs a stronger than normal stimulus to fire (relative refractory period). The absolute period lasts while the Na⁺ channels are open or inactivated; the relative period follows while K⁺ is still leaving. It keeps spikes separate and makes the impulse travel one way along the axon.
What happens during depolarization and repolarization?
In depolarization, voltage-gated Na⁺ channels open and Na⁺ rushes in, so the inside of the cell turns from −70 mV to about +30 mV; in repolarization, voltage-gated K⁺ channels open and K⁺ flows out, bringing it back down. Na⁺ moves in on the rising edge of the graph and K⁺ moves out on the falling edge.
What causes hyperpolarization after an action potential?
The voltage-gated K⁺ channels close a little late, so K⁺ keeps leaving the cell after the membrane is back at −70 mV. The potential dips below rest toward the K⁺ equilibrium potential, then the channels close and leak channels and the Na⁺/K⁺ pump return it to −70 mV.
What is the threshold potential?
The membrane potential, about −55 mV in a typical neuron, at which enough voltage-gated Na⁺ channels open for depolarization to keep itself going. Below it, a stimulus fades as a graded potential; at or above it, a full action potential fires — the all-or-none rule.
What is the difference between a neuron and a cardiac action potential?
A ventricular muscle action potential lasts about 250 to 300 ms instead of about 2 ms, starts from about −90 mV instead of −70 mV and has a long plateau (phase 2) while Ca²⁺ enters through slow channels. The plateau gives heart muscle a refractory period of about 250 ms, so it cannot be re-excited before it has contracted.
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