Ion Responsible for Neuron Depolarization

Neural communication involves a series of events that lead to the transmission of signals within the nervous system. When a neuron is activated, an electrochemical process occurs, allowing it to send a message to another neuron. This process is dependent on various ions moving across the neuron's membrane. The area of this process is highly regulated, as certain ions play crucial roles in determining whether the neuron will fire an action potential.

Which of the following ions is primarily responsible for depolarizing the neuron's membrane during an action potential?