Action potential
A brief voltage change propagates along an excitable cell’s membrane.
Definition
An action potential is a rapidly regenerating electrical event produced by coordinated changes in membrane ion conductance.
How to understand it
In the standard neuron model, sufficient depolarization initiates a spike, voltage-gated channels change ion movement, and the membrane returns toward its resting condition. The event propagates along the axon. Calling the spike all-or-none concerns its generation; it does not mean that every input produces a spike or that every neuron is continuously active.
Information is not generally represented by making each spike arbitrarily taller. Timing and patterns of spikes across cells matter. For introductory reasoning, distinguish the event traveling along an axon from the local inputs that help initiate it and from chemical signaling at a terminal. These are related steps, but naming one does not explain the others.
Evidence: (Spielman et al., 2020); (Noba: Neurons, n.d.); (Noba: The Brain and Nervous System, n.d.)
Interpreting two invented traces
Teaching scenario
A teacher sketches two voltage recordings from the same hypothetical neuron. Each contains spikes of similar height, but one has more spikes during the illustrated interval. Students describe the difference in the activity pattern without saying that the second recording contains “stronger individual thoughts.” The drawings teach the distinction between a discrete cellular event and the broader code a nervous system might use.
Constructed for learning. This scenario is not a report of an empirical finding or a diagnosis.
Common confusion: Graded potential
A graded potential varies in size locally; an action potential regenerates as it propagates.
Evidence: (Spielman et al., 2020); (Noba: Neurons, n.d.); (Noba: The Brain and Nervous System, n.d.)
Limits of the concept
- Threshold and waveform vary across cell types and conditions.
- All-or-none spikes do not make behavior, perception, or synaptic inputs all-or-none.
Evidence: (Spielman et al., 2020); (Noba: Neurons, n.d.); (Noba: The Brain and Nervous System, n.d.)
Textbook connection
Direct coveragePsychology 2e: 3.2 Cells of the Nervous System
Direct threshold, depolarization, repolarization, and all-or-none coverage.
Supplementary concepts may extend beyond this section. The source notes below identify the evidence for those details.
Related concepts
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Sources and inspection notes
Checked October 21, 2026. An inspection date is not a source publication date. Definitions and scenarios on this page are original teaching explanations.
- Noba: Neurons. (n.d.). https://nobaproject.com/modules/neuronsCell anatomy, graded inputs, action potentials, and receptor-dependent synaptic signaling; no precise cell counts used.
Opened and inspected on 21 October 2026. Academic teaching synthesis; not a primary experiment.
- Noba: The brain and nervous system. (n.d.). https://nobaproject.com/modules/the-brain-and-nervous-systemNeuron parts, nerve bundles, cellular signals, and distinct explanatory scales.
Opened and inspected on 21 October 2026. Introductory academic synthesis; dated evolutionary rhetoric and numerical counts not used.
- Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. https://openstax.org/books/psychology-2e/pages/3-2-cells-of-the-nervous-systemCourse textbook section
Opened actual subsection on 21 October 2026; title and URL verified. Course textbook, not independent primary evidence.