Ligand-gated channels are activated upon binding a chemical messenger such as a neurotransmitter. Na channel inactivate quickly. At any instant in time, the RP is caused by an imbalance of negative and positive charges on either side of the membrane. Permeability differences of these two ions. The Equilibrium Potential 1.
Ions diffuse through open channels down electrochemical gradients.
The Nernst Equation relates the chemical and electrical gradients for a single ion. It can be simplified for a positive ion at 37deg. If there is only one ion permeable to the membrane, this equation describes the membrane potential. At an ion's Equilibrium Potential there is no net flux across the membrane because the chemical gradient is balanced by an opposing electrical gradient. Nerve and muscle cells are permeable to mainly three ions, Na, K and Cl , each with its own Nernst potential.