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The all-or-none principle means that an action potential:

AGrows steadily weaker as it travels along the axon
BCan be halted midway if the input signal stops early
CEither fires at full strength or does not fire at all
DVaries in size according to how strong the stimulus is
Answer & Solution
Correct answer: C. Either fires at full strength or does not fire at all
1. An incoming signal is either sufficient or insufficient to reach the threshold of excitation, with no in-between. 2. Once started, there is no turning off an action potential, which the chapter compares to a lit firecracker fuse. 3. The signal is recreated at its full strength at every point along the axon rather than fading with distance. 4. That is why an injury to a distant toe is perceived as just as painful as one to the nose, which rules out options A and D. _Source: OpenStax Psychology (1st ed., CC BY 4.0), Ch 3 "Biopsychology", §3.2 Cells of the Nervous System_
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