Electroconduction System of the Heart

The electroconduction system of the heart is a complicated system of the body that begins in the right atrium at the sinoatrial (SA) node. The SA node, a small bundle of cells located on the back wall of the right atrium, serves as a pacemaker for the heart. The SA node fires, by self-excitation, an electrical impulse that is spread across the right atrium and to the left atrium by the Bachman's bundle so that both atria can contract at the same time.

The contraction of the atria forces blood from the atria to the ventricles through their respective valves. The impulse that is started at the SA node then travels to the atrioventricular (AV) node. The AV node acts as a delay line to slow down the action potential along the internal electroconduction system.

This is done so that all of the blood from the atria can be emptied into the ventricles before the ventricles contract. The action potential then travels from the AV node to the Purkinje fibers. The Purkinje fibers are arranged in two bundles, one bundle branching to the muscle in the right ventricle and the other branching to the muscles in the left ventricles.

The action potential moves through these fibers very rapidly and spreads throughout the ventricles at two to four meters per second. This causes the ventricles to pump fast and hard. This forces the blood through their respective valves out to the body at an extremely fast rate.

The contraction of the ventricles is known as systole. The relaxation of the ventricles is known as diastole.

The electroconduction of the heart starting at the SA node and traveling through the AV node to the Purkinje fibers creates a mass electrical signal that can be detected by placing electrodes on a patient's chest or extremities.

This electrical signal can be mechanically plotted and the resultant plot is called an electrocardiogram (ECG). The letters on the ECG represent different functions that occur in the heart. The P-wave indicates atrial contraction. Ventricular contraction is represented by the QRS complex, and the T-wave indicates ventricular repolarization.

Exercise 26. Answer the following questions.

1. Where does the electroconduction system begin?

2. Where is the SA node located?

3. What does the SA node serve as?

4. What does the contraction of the atria force?

5. What is the function of the SA node?

6. Where does the action of the potential travel to?

7. How are the Purkinje fibers arranged in?

8. What is a systole?

9. What is a diastole?

10. What does the electroconduction of the heart create?

11. What is called an electrocardiogram?

12. What does the P-wave indicate?

13. What is ventricular contraction represented by?

Exercise 27. Finish the sentences.

1. The relaxation of the ventricles is known as ___________.

2. A mass electrical signal that can be detected by placing electrodes on a patient's _______________.

3. The action potential moves through these fibers very ________.

4. The T-wave indicates ventricular ________________.

5. The ventricles pump _________ ________.

6. The action potential then travels from the AV node to ________ ________.

7. The electroconduction system of the heart is a complicated system of __________.

8. The contraction of the atria forces blood from the atria to the ventricles through ___ _______ ________.

Exercise 28. Open brackets and use a proper grammar form.

1. The letters on the ECG …..(to represent) different functions that occur in the heart.

2. The P-wave …….(to indicate) atrial contraction.

3. The Purkinje fibers ……(to arrange) in two bundles.

4. The contraction of the ventricles …..(to know) as systole.

5. The impulse …….(to travel) to the atrioventricular (AV) node.

6. The SA node …..(to locate) on the back wall of the right atrium.

7. The SA node serves as a pacemaker for the heart.

8. The blood from the atria …….(to empty) into the ventricles before the ventricles contract.

9. The electroconduction system of the heart ….(to begin) in the right atrium at the sinoatrial (SA) node.

Exercise 29. Read and translate the text.