The plasma membrane of axon is called axolemma. The potassium and sodium leak channels leak the sodium and potassium ions inside the cell respectively. The leak channels provide the constant movement of ions across the membrane. Potassium and sodium ions are positively charged, thus entry of positively charged ions inside the cell makes the cell more positively charged than the environment outside the cell. The environment outside the cell becomes more negatively charged. This leads in the negative membrane potential of axolemma.
