Final answer:
The unequal distribution of ions across the plasma membrane creates a membrane potential, caused by selective permeability and maintained by the Coulomb force, resulting in an electrochemical gradient essential for nerve impulses.
Step-by-step explanation:
The unequal distribution of positive and negative ions across the plasma membrane is reflected in the formation of a voltage, or membrane potential, across the cell membrane. In the resting state, certain ions like Na+ (sodium) are more concentrated outside the cell, while others like K+ (potassium) are more concentrated inside. The semipermeable nature of the plasma membrane allows for the selective movement of ions, contributing to this separation of charges. The membrane potential is created by the differing concentrations of ions, and is maintained by the Coulomb force preventing ions from fully equalizing their concentrations across the membrane due to repulsion of like charges and attraction of opposite charges.
Furthermore, the inside of the cell is negatively charged relative to the outside, helping to drive the movement of cations into the cell and anions out of the cell. This results in an electrochemical gradient that combines both the ions' concentration gradient and the electrical force of the membrane potential. This gradient plays a crucial role in physiological processes such as the generation of nerve impulses.