Re: If they say a cell's membrane potential increases, what does it mean?

Leslie,

Thanks for this interesting question.

The answer depends on which side of the membrane your reference point is.

Living cells use energy to maintain an electric charge difference across the lipid bilayer membrane. The potential is generated by distribution of more sodium ions Na+ outside the cell and retaining more Chloride ions CL- inside the cell.

Of course there are numerous other positive ions including potassium, calcium, magnesium; and negative ions like bicarbonate, sulfate, etc in the mix.

When cells die they lose this charge difference, so you could say life is the process of maintaining disequilibrium. One's cells should never go into equilibrium which seems to be so counterintuitive considering the social or behavioral concepts of equilibrium....well anyway.

This difference is called a potential and can be measured in mili Volts. A resting nerve cell has a membrane potential of 60 - 70 mV.

At rest, there is a relative excess of positive charges outside and negative charges inside the membrane of a nerve cell. When a nerve conducts a signal down its axon there is a wave of depolarization of this potential so the relative positivity of the outside and negativity of the inside shifts and becomes neutral or reverses as the wave propagates down the axon.

So, in answer to your question, when there is a rise in potential of a cell the outside becomes more positive and the inside becomes more negative.

After a lot of the details of cell potential was worked out in nerve cells (the squid axon is one that is large and very useful to model this), scientists found that numerous other cells also display potential changes so you can think of your body as buzzing with electricity.

Sharks have sensors on their skin for electric currents so don't buzz to strongly.

Below this message are some useful URLs that will link you to more useful information about membrane potentials.

I hope you found this helpful.

http://www.ifisiol.unam .mx/Brain/mempot.htm

http://en.wikipedia .org/wiki/Membrane_potential

http://lessons.harveyproject.org/dev elopment/nervous_system/cell_neuro/memb_potl/K_electrode/Nernst.html