Depolarization and repolarization

Question 1

What is an action potential?

Answer 1

A sequence of changes in the membrane potential that occurs when an excitable cell is stimulated.

Question 2

Define depolarization in the context of cardiac muscle fibers.

Answer 2

The process of discharging resting cardiac muscle fibers by means of an electrical impulse that stimulates contraction.

Question 3

What do chemical pumps inside myocardial cells maintain?

Answer 3

Ion concentration within the cell, creating an electrical gradient across the cell membrane.

Question 4

What is the net internal charge of a resting (polarized) cell?

Answer 4

−90 millivolts (mV) relative to the outside of the cell.

Question 5

What happens to the cell wall when it is stimulated?

Answer 5

Becomes more permeable as specialized channels open, allowing sodium ions (Na+) to rush into the cell.

Question 6

How does the reversal of the cell’s electrical charge occur?

Answer 6

Begins at one point in the cell wall and spreads in a wave until the cell has been completely depolarized.

Question 7

What initiates repolarization in a cell?

Answer 7

The closing of sodium and calcium channels.

Question 8

What role do potassium channels play during repolarization?

Answer 8

Allow the rapid escape of potassium ions (K+) from the cell to restore a negative charge.