What are the ionic mechanisms of resting potentials?

To understand the ionic mechanisms of resting potential, it is important to first understand that: 

• Ions are unevenly distributed on the inside and outside of cells
• Cell membranes are selectively permeable to different ions

Because the cell membrane is highly permeable to potassium ions (K+), these ions play a crucial role in the resting potential. There is a high concentration of K+ ([K+]i) inside the cell and a low concentration of K+ ([K+]o) outside the cell. Due to this concentration gradient, K+ naturally diffuses from the inside to the outside of the cell. 

As positive K+ ions leave the cell, negatively charged ions get left behind, creating an electrical force that pulls the K+ ions back inside. This inward electrical force counteracts the outward diffusion force, creating an equilibrium where the concentration force moving K+ out balances the electrical force pulling it in. This balance is known as the Nernst Equilibrium Potential.

Sodium ions (Na+) also contribute to the resting potential. The high concentration of Na+ outside the cell and the low concentration inside create a chemical driving force for Na+ to enter the cell. Additionally, the negative charge inside the cell attracts positive Na+ ions. If the cell membrane is slightly permeable to Na+, Na+ will enter the cell, causing the membrane potential to be more depolarized than the K+ equilibrium potential alone would predict.