What is the ascending (initial) portion of an action potential observed in a cell is caused by?
A. Sodium influx into the cell.
B. Sodium efflux out of the cell.
C. Potassium influx into the cell.
D. Potassium efflux out of the cell.
E. Potassium influx out of the cell.
A large sodium (NA+) influx into the cell will result in the resting potential (-50 mV) becoming more positive and thereby initiates the action potential. Potassium is already in very high concentration (~141 mEq/ liter) intracellularly and will not enter the cell.