This one is tough. A typical cell has fluid outside of it called extracellular fluid (tissue fluid or interstitium) and fluid inside of it called intracellular fluid (cytosol). These fluids have differing combinations of solute dissolved in them, and the cell membrane provides a selectively permeable membrane that controls what is outside the cell and what is inside the cell. One of the things controlled is the electrical potential (voltage). It does this using gated ion channels. Gated ion channels may be open or closed during various situation. In a resting cell, the voltage across the membrane is called the resting membrane potential. This is about -70 millivolts (mV) in a typical brain cell (neuron). The -70mV just means that the INSIDE of the cell is -70mV LESS than the OUTSIDE. There are 4 ways to change this number to make it more positive (greater than or equal to -69mV) and there are 4 ways to change this number to make it more negative (less than or equal to -71mV). These changes involve either opening a gated ion channel that is closed, or closing a gated ion channel that is open.
Can you name these 8 changes?