The all or none law of nerve impulse conduction states that
- A. a stronger stimulus produces a larger action potential
- B. an impulse can travel in either direction along the axon
- C. every stimulus produces an impulse regardless of its strength
- D. any stimulus at or above threshold produces an action potential of the same size
Explanation
Once threshold is reached the sodium channels open fully, so the size of the spike is fixed by the ion gradients and not by how strong the stimulus was. Stimulus intensity is coded instead by the frequency of impulses and by how many neurones are firing. A stimulus below threshold produces no impulse at all, so it is not true that every stimulus produces one.
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