The Cardiac Conduction System

1. The Cardiac Conduction System Chapter 11 pp-354-358

2. The Cardiac Conduction System Definition: Specialized cardiac muscle tissue with fibers that initiate and distribute impulses throughout the myocardium. (muscle layer of the heart) Purpose: Coordinates the events of the cardiac cycle

3. Review: What is the cardiac cycle? The rhythmic contraction (systole) and relaxation (diastole) of the chambers of the heart that corresponds to one heartbeat. During the cardiac cycle, blood is pumped out of the heart into the aorta and the pulmonary artery, and blood reenters the heart from the venae cavae and the pulmonary veins. Link

4. Parts of the cardiac conduction system

5. Function of parts • S-A node- “Pacemaker” -bundle of cardiac muscle tissue -sends impulses that cause the atria to contract -Passes impulses to the A-V node/A-V bundle Did you know the heart can beat outside of the body because of the S-A node? Click on the heart to watch.

6. A-V node, Junctional fibers, A-V bundle -slow impulses until atria are done contracting -send impulses on to Purkinje fibers • Purkinje fibers -Deliver impulses to muscle tissue of ventricles, causing ventricles to contract and blood to be forced through pulmonary artery and aorta

7. Electrocardiogram (ECG) • Recording of the electrical changes that occur in the myocardium during a cardiac cycle.

8. When do the atria relax? During the QRS wave.

9. Relating the cardiac conduction system to the cardiac cycle Click on the heart to watch a video on the cardiac conduction system. Are the cells that create heart beats part of the nervous system?

10. Regulation of the Cardiac Cycle • One cardiac cycle takes .85 seconds which results in a heart rate of 70 beats per minute. • However, the volume of blood pumped must change to accommodate cellular requirements. -So… although the S-A node can work on it’s own, the autonomic nervous system plays a role in the rate of the cardiac cycle.

11. An example of how the nervous system over-rides the cardiac conduction system

12. What other sensory receptors will the autonomic nervous system use to monitor and adjust heart rate? • Chemoreceptors- can you give an example? • High levels of carbon dioxide increase heart rate- Why? It is a waste product that must be pumped to the lungs for removal. • Thermoreceptors- can you give an example? • When the body is overheated the heart beats faster- Why? To increase the rate at which heat is move through the body to the surface of the skin for cooling.

13. Play the EKG game: • The goal of the game is to perform an EKG in order to diagnose 4 patients heart health. • Follow the directions and show your score to your teacher. • Click on the heart to link to the game.