AP Psychology Practice Test

What triggers an action potential?

1. The release of hormones into the bloodstream

2. The movement of positively charged atoms in and out of axon channels

3. The physical movement of the neuron

4. The reception of a signal by the dendrites

The correct answer is: The movement of positively charged atoms in and out of axon channels

The concept of action potentials is fundamental to understanding how neurons communicate. An action potential is triggered when there is a change in the electrical charge across the neuron's membrane. Specifically, this occurs due to the movement of positively charged ions, such as sodium and potassium, through ion channels in the axon. When a neuron receives enough stimulation, ion channels open, allowing sodium ions to rush into the cell, leading to depolarization. After reaching a certain threshold, this change in charge propagates along the axon as an action potential. The other options describe processes or events that do not directly initiate the action potential. For instance, while hormones can influence overall neuronal function and mood, they do not specifically trigger the biological mechanism of an action potential in individual neurons. Similarly, while physical movement can be an effect of neuron firing, the movement of the neuron itself does not cause an action potential. Reception of signals at the dendrites is essential for bringing the neuron to the threshold of firing but is not the primary mechanism for the actual triggering of the action potential itself.