A common feature of action potentials is that they
A) cause the membrane to hyperpolarize and then depolarize.
B) can undergo temporal and spatial summation.
C) are triggered by a depolarization that reaches threshold.
D) move at the same speed along all axons.
E) require the diffusion of Na+ and K+ through ligand-gated channels to propagate.

Question

Quizplus · Accepted Answer

Action potentials are triggered when the membrane potential of a neuron reaches a certain threshold, typically around -55 to -40 mV. This depolarization opens voltage-gated ion channels, allowing an influx of Na+ ions and the initiation of the action potential.

Answer: B
 Temporal and spatial summation are key features of the generation and propagation of action potentials. Temporal summation refers to the buildup of depolarizations over time, whereas spatial summation occurs when depolarizations from multiple input sites sum together to reach threshold.

Answer: E
 The propagation of an action potential relies on the diffusion of ions, particularly Na+ and K+, through ligand-gated channels. As Na+ ions enter the neuron, the membrane depolarizes, allowing adjacent voltage-gated ion channels to open and propagate the action potential down the length of the axon.

Therefore, choices C and B are correct. Choice E is incorrect because it is not the mechanism by which action potentials propagate.

A Common Feature of Action Potentials Is That They