AEMCA Practice Exam

What is depolarization in terms of cellular activity?

1. The action of sodium channels opening

2. The action of potassium channels opening

3. Closure of sodium channels

4. The resting state of a neuron

The correct answer is: The action of sodium channels opening

Depolarization refers to the process during cellular activity, particularly in neurons, where the membrane potential becomes less negative (or more positive) than the resting state. This change is predominantly due to the opening of sodium channels in the neuron's membrane. When these channels open, sodium ions (Na+) flow into the cell, driven by both a concentration gradient and the electrical gradient, leading to a rapid increase in the interior voltage of the neuron. This shift from a negative resting potential toward a positive potential is essential for generating action potentials, which are critical for transmitting signals along neurons. The other options, while relevant to cellular activity, describe different processes. The opening of potassium channels would typically lead to repolarization rather than depolarization, as potassium ions would exit the cell, making the internal environment more negative again. Closure of sodium channels does not initiate depolarization; instead, it marks the end of this phase during repolarization. Lastly, the resting state of a neuron characterizes the period before any stimulation occurs, which is distinctly different from the active phase of depolarization.