Chapter 19

The Circulatory System: Heart

Topic of lesson

Cardiac Conduction System: The heartbeat is coordinated by a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract.

Learning objectives

At the end of the lesson, the student should be able to

• describe the heart’s pacemaker and internal electrical conduction system;
• describe the nerve supply to the heart and explain its role.

Pre-assignment

Watch the video: Cardiac Conduction System and Understanding ECG, Animation

Activity

1. Teacher hands out a normal Electrocardiogram report and let students check the pattern.
2. Cardiac conduction is the driving force behind the cardiac cycle. This cycle contains a series of events that occur when the heart beats. Students try to explain what is a cardiac cycle according to what they have learned from previous lessons.
3. Students use the Quizlet Diagram on their iPads to learn the terms of conduction system and finish labeling the Cardiac Conduction System worksheet.
4. Teacher introduces the Cardiac Conduction System generates and conducts rhythmic electrical signals in the following order:
   1. SA node fires
   2. Excitation spreads through atrial myocardium
   3. AV node fires
   4. Excitation spreads down AV bundle
   5. Subendocardial conducting network (Purkinje fibers) distributes excitation through ventricular myocardium
5. Although the heart has its own pacemaker, it is also affected by sympathetic and parasympathetic nerves, which alters heart rate and contractility. Students brainstorm what factors may change the heart rate.
6. Teacher uses the chart about parasympathetic and sympathetic nerves to help students review what they have learned in Chapter 15 about the autonomic nervous system.
7. Students do research on real case about extreme high or low heart rate, what are the causes and how to treat them safely, then share within the group.
8. Two students record each other summarizing what he or she has learned in this lesson and post it into their personal digital portfolio.

Resources

• Science notebook for taking notes
• A normal Electrocardiogram report for checking the pattern
• Cardiac conduction system worksheet for labeling the parts
• iPads for studying Quizlet, doing research and recording