A 9.0-nm-thick cell membrane undergoes an action potential that follows the curve in the table on page 748 . What is the strength of the electric field inside the membrane just before the action potential and at the peak of the depolarization?

The action potential Depolarization Repolarization Reestablishing resting potential + + Na+ opyright K+ + + AV membrane (mV) +40- Diffusion of ions reestablishes the resting potential. (ms) 1 (ms) 0 2 3 -70- AVmembrane (mV) A stimulus at this time +40- causes a quick rise in membrane potential. (ms) AV membrane (mV) The membrane potential drops rapidly, overshooting its initial value. +40- -70- 0 2 201 A cell depolarizes when a stimulus causes the opening of the sodium channels. The concentration of sodium ions is much higher outside the cell, so positive sodium ions flow into the cell, rapidly raising its potential to 40 mV, at which point the sodium channels close. -70- 1 2 The cell repolarizes as the potassium channels open. The higher potassium concentration inside the cell drives these ions out of the cell. The potassium channels close when the membrane potential reaches about -80 mV, slightly less than the resting potential. The reestablishment of the resting potential after the sodium and potassium channels close is a relatively slow process controlled by the motion of ions across the membrane.