what is a membrane potential?

Answer 1

Membrane potenial - The charge difference between the cytoplasm and extracellular fluid in all cells, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

Answer 2

The membrane potential is the difference in electrical charge between the inside of a membrane and the outside. This arises due to differences in ion concentrations on either side of the membrane which occurs because of selective permeability of the membrane to specific ions.

Cell membranes have distinct potential differences across them, as do mitochondria - for example.

Answer 3

Membrane potential is defined as charge difference between inside and outside of the cell membrane. The charge is created by having a difference in ion concentration inside and outside the cell. For example, neurons have membrane potential achived by a difference in concentration of potassium ions and sodium ions from inside and outside the cell. It is not necessary for certaind ions to be outside the cell membrane and the other ions inside the cell membrane. Ions can switch places. The movement of ions is usually by simple diffusion. However, in some cells, ATP-as is used to pump in/out ions to stabilize the charge.

Answer 4

The two previous answers are good, but moving enough ions to make a noticeable potential will require active transport (which takes energy). Cells which do this have ion pumps embedded in the cell membrane.