membrane potential?

Question

if I have a nerve cell with a membrane potential of 0mV, and if I make it permeable only to Na+ ions. WHat would happen? Does it reach the membrane potential for Na+ and the stimulus goes on and on?

THank you so much, you really helped me. All your answers are nicely thought

Answer 1

What I believe would happen is that the Na+ ions would move into the cell and it would become further depolarized, even to the point of an action potential. However, there would need to be hyperpolarization of the cell again in order to have more APs. What you'd have is a cell remaining in a refractory state, if it's not allowed to go lower than 0 mV.

After a while, though, there could be a levelling of the gradients on either side of the membrane, even though Na+ channels would be open.

Answer 2

If you start with a cell at membrane potential of 0, assuming physiologic concentrations of all ions, selective permeability to Na+ ions will cause influx of these Na+ ions, down the concentration gradient, and down the charge gradient as it flows into the cell. This will make the inside of the cell more positive, and the potential across the membrane will reach and settle at the equilibrium potential of Na+.

Answer 3

That would depend on whether the membrane potential was based solely on the sodium. For example the membrane potential could be zero, but the sodium could built up outside the cell, with an equal amount of potassium inside.

If only the sodium gates opened, then the sodium would rush into the cell just based on conc. gradients and further depolarize the cell.

Answer 4

Making the membrane permeable to sodium ions would cause depolarisation -- in other words, an action potential. So that nerve would be depolariased until it's able to repolarise. During that time it wouldn't be able to conduct another action potential -- it has to repolarise first.