Electrical Potential of a Cardiac Cell

The cardiac system is a closed-loop hydraulic system that is constantly contracting and relaxing, pumping blood throughout the body. The cell wall of cardiac cells is a semipermeable membrane that allows the passage of some ions while restricting others. The cell membranes, at rest, tend to be more permeable to some ions than others. The movement of ions across a membrane changes the concentration of ions within and outside the cells which results in an action potential. This action potential of the cell results in a depolarizing and repolarizing of the cell itself. In a cardiac cell the action potential is caused by the movement of sodium and potassium at different rates. A phenomenon in a cardiac cell called the sodium-potassium pump moves sodium outside the cell and potassium inside. This results in a difference of ion concentration which in turn results in an electrical potential.

At rest the concentration of positive sodium ions outside the cell is higher than the concentration of sodium inside the cell which results in the electrical potential. This electrical potential is negative with respect to the outside resulting in a resting potential of a negative seventy to ninety millivolts. When the cell is stimulated, the sodium ions rush into the cell forcing potassium out which results in the action potential. This action potential results in the inside of the cell being twenty to forty millivolts more positive than the outside and the cell is said to have depolarized.

The cell is repolarized when the sodium-potassium pump pumps the sodium back out of the cell and the potassium back into the cell which resets the cell so it can be depolarized again. An ionic electrical conduction is started by the depolarization of one cell which in turn triggers the next cell causing an action potential. This situation causes a triggering of cells in a cascade effect making all the cells depolarized.

Exercise 22. Give Ukrainian equivalents to the following words and word combinations.

To change the concentration of ions, semipermeable membrane, to restrict, outside the cell, to pump blood, passage of some ions, cardiac cell, in turn, difference of ion concentration, electrical potential, within and outside the cells, resting potential, to rush into the cell, with respect to, ionic electrical conduction, cascade effect, concentration of positive sodium ions, sodium-potassium pump, action potential.

Exercise 23. Fill the blanks in the following sentences.

electrical conduction	positive sodium ions
heart	cascade effect
closed-loop	within and outside
allows	electrical potential
depolarizing	potassium

1. The movement of ions across a membrane changes the concentration of ions ………..the cells which results in an action potential.

2. The sodium-potassium pump pumps the sodium back out of the cell and the ……….back into the cell.

3. The …….. pumps blood throughout the body.

4. This results in a difference of ion concentration which in turn results in an electrical potential.

5. At rest the concentration of ………………….outside the cell is higher.

6. The cardiac system is a ……………………hydraulic system.

7. This situation causes a triggering of cells in a ……………………….

8. This action potential of the cell results in a ………………and repolarizing of the cell itself.

9. An ionic …………………..is started by the depolarization of one cell.

10. A semipermeable membrane ………..the passage of some ions

Exercise 24. Speak about a phenomenon in a cardiac cell.

Exercise 25. Read and translate the text.