Selective permeability of the plasma membrane. As charged molecules, ions cannot readily diffuse through the hydrophobic core of the plasma membrane's phospholipid bilayer.
Ions can only cross membranes by carrier-mediated transport or by passing through ion channels.
Integral transmembrane protein that allows a specific ion to cross the membrane. Membrane permeability to each ion is a function of the type and number of ion channels. Pump potassium into the cell, restoring its concentration gradient. All cells in the body exhibit the properties of membrane potential described above. However, only neurons and muscle cells can change their membrane potentials in response to stimuli.