What triggers depolarization?

Hint: Depolarization is the process of change that occurs within the cell during the cell undergoes the shift in electric charge distribution and provides less negative charge inside the cell. Depolarization is an important process in many cells and it provides communication between the cells. It is responsible for the overall physiology of an organism. Nerve cells depolarized by the several stimuli.

Complete answer:
Stimuli is used to open the several sodium channels. In neurons sodium ions are presented inside and outside of the neurons. Stimuli like chemical, light, physical or electric stimulus provide the positive potential in the neuron. If the positive potential is higher than the negative potential then the threshold potential will produce. This threshold potential is used to open the sodium channels. During the opening of channels, the positive ions are moved into the channel and depolarization will occur. So, this is the triggering process of depolarization.
Depolarization occurs during the open or close of ion channels. It also alters the type of ions to enter or exit from the cell. Stimulus first opens the sodium channel. Because sodium is positive and inside the neuron lots of negative ions are present so ions are rushing towards the neuron. So, the neuron becomes positively charged and becomes depolarized.

Note:
During the depolarization process membrane potential is changed rapidly from negative to positive. After the polarization, the cell interior is charged as positive. Depolarization is called the active potential and it is dependent on the two types of channels called the sodium and potential channels. The voltage gated sodium channel actually has two gates. Movement of a cell membrane potential to more positively is called depolarization.