The following incomplete statements refer to a muscle cell in the resting, or polarized, state just before stimulation. Complete each statement by choosing the correct response from the key choices and entering the appropriate letter in the answer blanks. Key Choices:
A. Na+ diffuses out of the cell
B. K diffuses out of the cell
C. Na+ diffuses into the cell
D. K+ diffuses into the cell
E. Inside the cell
F. Outside the cell
G. Relative ionic concentrations on the two sides of the membrane during rest
H. Electrical conditions
I. Activation of the sodium-potassium pump, which moves K+ into the cell and Na+ out of the cell
J. Activation of the sodium-potassium pump, which moves Na+ into the cell and K+ out of the cell
1. There is a greater concentration of Na+ _(1) and there is a greater concentration of K+ _(2). When the stimulus is delivered, the permeability of the membrane is changed, initiating the depolarization of the membrane. Almost as soon as the depolarization wave begins, a repolarization wave follows it across the membrane. This occurs as repolarization restores the (3) of the resting cell. The (4) is reestablished by (5).
