AAMC FL Practice Exam 2026 – Complete Prep Test

In the context of axons and neuronal activity, the correct answer highlights that axons have a predominantly negative charge at rest due to the distribution of ions inside and outside the neuron. At rest, most neurons maintain a resting membrane potential of about -70 mV, which indicates a negative charge relative to the outside of the cell. This negativity is primarily the result of higher concentrations of potassium ions (K+) inside the cell and sodium ions (Na+) outside of it, which creates an electrochemical gradient.

During an action potential, the charge within the axon temporarily shifts towards a positive value as sodium channels open and allow Na+ to flow into the cell. However, the premise of the question is focused on the state of the axon at rest, emphasizing its negative charge. This characteristic is crucial for the proper function of neurons, facilitating the generation and propagation of action potentials necessary for signal transmission throughout the nervous system.