What is the threshold?

The minimum stimulus strength needed to trigger an action potential; below it the neuron does not fire.

Is an action potential all-or-none?

Yes. Once threshold is reached the impulse fires at full strength; a stronger stimulus does not make a larger action potential.

Grade 12 · Biology

Neurons & the action potential

Why it matters

Nerve cells and the impulse.

Advanced20m readingPrerequisite: None

What is an action potential?

Short answer

An action potential is the rapid electrical signal a neuron uses to transmit information. At rest the inside of the neuron is negative; when a stimulus reaches threshold, sodium ions rush in and depolarize the membrane, then potassium ions leave to repolarize it. This wave of voltage change travels along the axon toward the synapse.

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Frequently asked questions

What is the threshold?: The minimum stimulus strength needed to trigger an action potential; below it the neuron does not fire.
Is an action potential all-or-none?: Yes. Once threshold is reached the impulse fires at full strength; a stronger stimulus does not make a larger action potential.

What is an action potential?

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Frequently asked questions