1. Conduction System GR 12 B

2. The Conduction System A. The cardiac muscle is autorhythmic, meaning it can contract without nerve impulses or hormones. B. These specialized cells are called nodes or nodal cells 1. Nodal cells, or pacemaker cells, are specialized cells that create an electrical impulse at a regular interval 2. These cells are connected to each other and to the conducting network

3. The Conduction System Nodal cells are divided into two groups a. Sinoatrial node (SA) i. Located in the wall of the right atrium, near the entrance of the superior vena cava ii. Generates an electrical impulse at approximately 70 to 80 impulses per minute

4. The Conduction System b. Atrioventricular node (AV) i. A second collection of pacemaker cells located at the point where the atria and ventricles meet ii. Cells in AV node generate an electrical impulse at a rate of 40 to 60 beats per minute

5. The Heart Rate 1. The SA node sets the heart rate at rest, many other factors change heart rate

6. The Heart Rate a. Autonomic nervous system (sympathetic and parasympathetic) has direct connection to SA and AV nodes and to the myocardium i.Sympathetic division can release neurotransmitters that increase heart rate and the force of contraction ii. Parasympathetic division can release a neurotransmitter via the vagus nerve to decrease heart rate and the force of contraction

7. The Heart Rate Ions, hormones, and body temperature can alter heart rate i. Fever increases heart rate due to an increased metabolic rate ii.Epinephrine increases heart rate iii.Altered levels of sodium, potassium, or calcium (ions) can alter heart activity Low potassium can lead to a weak heartbeat High calcium can prolong heart muscle contractions to the point where the heart can stop beating

8. The Heart Rate Age, sex, and exercise can all impact heart rate i. Healthy female heart rate is 72 to 80 bpm ii. Healthy male heart rate is 64 to 72 bpm

9. Movement of electrical impulses 1. Movement of electrical impulse in the myocardium is done by specialized conducting cells 2. The conducting cells distribute the electrical impulse in such a way that a. The right and left atria contract together first b. The right and left ventricles contract together next i. Ventricular contraction spreads from the apex to the base of the heart

10. Movement of electrical impulses a. Once an electric impulse is generated at the SA node, it travels to the AV node b. Once the charge hits the AV node, it travels through the AV bundle, or bundle of His c. The impulse travels down the right and left bundle branch in the interventricular septum

11. Movement of electrical impulses d. These branches spread across the inner surface of both ventricles e. The impulse travels into the Purkinje cells to carry the impulse to the contractile muscle cells of the ventricles

12. Watch a video on the conduction system Conducting System Of The Heart – YouTube