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.
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.