What is meant by “all or none” in regards to action potentials.
The correct answer and explanation is:
The phrase “all or none” in regards to action potentials means that once a neuron’s membrane potential reaches a certain threshold, an action potential either fires completely or does not fire at all—there is no partial or weaker action potential.
Explanation:
- When a neuron receives a strong enough stimulus, the membrane potential depolarizes to a threshold level (usually around -55 mV).
- If this threshold is reached, voltage-gated sodium channels open, triggering a rapid, full depolarization and the generation of an action potential.
- If the stimulus is below the threshold, the neuron does not generate an action potential.
- The strength or size of the action potential is always the same for a given neuron; it doesn’t get “bigger” or “smaller” depending on stimulus strength once the threshold is reached.
- The frequency of action potentials can vary with stimulus intensity, but each individual action potential follows the all-or-none rule.
In short:
- All: Full action potential fires when threshold is met.
- None: No action potential if threshold is not met.
This ensures clear, reliable communication in the nervous system without ambiguous or partial signals.