In an atom, a positive charge occurs when an atom has more protons than electrons. The proton is what determines its positive charge. It is denoted with a plus (+) sign. It attracts negative charges and repels other positive charges.

This difference in charge is called the cell's membrane potential. In the process of depolarization, the negative internal charge of the cell temporarily becomes more positive (less negative). This shift from a negative to a more positive membrane potential occurs during several processes, including an action potential. During an action potential, the depolarization is so large that the potential difference across the cell membrane briefly reverses polarity, with the inside of the cell becoming positively charged.