- A All neurons throughout the body fire simultaneously together
- B An impulse is either at full strength or does not occur at all
- C Impulses can vary continuously in strength depending on stimulus size
- D Only motor neurons obey this principle, unlike sensory neurons
Correct answer: B. An impulse is either at full strength or does not occur at all
Explanation: All-or-nothing principle: if threshold is reached, a full action potential fires; if not reached, no impulse. Impulse is always full strength.
Concept context
Brain, spinal cord, neurons, reflex arcs, and sense organs.