Final answer:
The exchange of electrolytes such as sodium and potassium across a cell membrane is necessary for an electrical impulse to occur, through mechanisms like facilitated diffusion and active transport.
Step-by-step explanation:
The electrolytes have to exchange across a membrane for an electrical impulse to happen. This exchange typically involves ions like sodium (Na+) and potassium (K+), which are essential for the generation and propagation of electrical signals in nerve cells. These ions cannot freely pass through the nonpolar lipid bilayer of cell membranes because they are charged. Instead, they move through membrane proteins that function as channels or pores. For example, Na+ ions can move down their concentration gradient from outside the cells to inside through sodium channels. This process is known as facilitated diffusion, a type of passive transport that does not require energy. However, there are scenarios where ions must move against their concentration gradient, requiring active transport, which uses energy in the form of ATP. Together, the concentration gradient and electrical gradient form the electrochemical gradient, which is critical for various cell functions such as nerve impulse transmission.