What is the process called when sodium ions rush into the cell causing the interior to become more positive?

The process described is known as depolarization. This occurs when sodium ions (Na+) enter the neuron through specialized ion channels, leading to a decrease in the negative charge inside the cell. As sodium ions flood into the cell, the internal environment becomes less negative (or more positive), moving towards a threshold that can initiate an action potential. This is a crucial step in the transmission of signals within the nervous system, as it allows the neuron to reach the threshold needed to fire and propagate a signal.

Hyperpolarization is the opposite process, where the interior of the cell becomes more negative relative to the outside, typically following an action potential. Polarization generally refers to the overall state of the cell membrane being maintained, while repolarization is the process that follows depolarization, occurring when potassium ions exit the cell to restore the negative charge after an action potential has occurred. Understanding these processes is essential in studying how neurons communicate and how signals are propagated in the nervous system.