Which term describes a neuron signal that travels along the axon without decreasing in magnitude?

• A. Graded potential
• B. Action potential
• C. Resting potential
• D. EPSP

Answer: (B)

Action potentials are signals that travel along a neuron's axon without decreasing in magnitude. This happens because they are all-or-none events that, once triggered at the axon hillock when threshold is reached, cause a rapid depolarization through the opening of voltage-gated Na+ channels. The signal is then regenerated at each successive patch of membrane as the next set of voltage-gated channels opens, so the peak voltage remains the same as it propagates. After depolarization, voltage-gated K+ channels open to repolarize (and briefly hyperpolarize) the membrane, but this does not diminish the strength of the signal as it moves. Graded potentials, such as EPSPs and other subthreshold changes, vary in size and decay with distance, so they do not maintain constant magnitude over long distances. Resting potential is the baseline membrane potential when the neuron is not signaling, and EPSPs are a type of graded potential that can help reach the threshold for an action potential but do not themselves travel without decrement.