1. May 8, 2015  Objective:  Describe how the cardiac cycle is regulated  Explain how a heart beat works  Journal: Has anyone had an EKG? What was it like? What do the lines mean?

2. ELECTRICAL PATHWAYS OF THE HEART

3. Autorhythmicity  The ability for the heart muscles to contract on their own

4. Nodal Cells  Also called pacemaker cells  Create an electrical impulse at a regular interval  Combine together to form nodes  SA Node: collection of pacemaker cells found in the wall of the right atrium near the entrance of the vena cava  AV Node: collection of pacemaker cells at the point where the atrium and ventricle meet

5. Typical Heart Beat Control  SA node usually dictates how fast the heart beats, but the AV node will take control if the SA node cannot generate an impulse  SA node sends its impulse to the AV node for distribution before the AV node can send out it’s own

6. How the Impulse Travels to Ventricles  SA Node generates an impulse  Travels to AV Node  Impulse travels down the Bundle of His within the interventricular septum  Bundle of His divides into the right bundle branch and the left bundle branch as it moves down the septum  Purkinje fibers carry the impulses from the bundle branches to the muscle cells of the ventricles and cause them to contract

7. Heart Rate Control Under Stress  Inotropism: When the body is under stress the sympathetic nervous system can release neurotransmitters to increase the heart rate and force of contraction  Vagus Nerves: the parasympathetic nervous system can release neurotransmitters to decrease the rate and force of contraction

8. Electrocardiogram (EKG)  Records the electric impulse traveling through the heart using surface detection  Three Waves:  P wave: impulse generated by the SA node and the depolarization of the atria before they contract  QRS Complex: depolarization of the ventricles that occurs right before they contract  T wave: repolarization of the ventricles while they are resting before the next contraction

9. EKG Abnormalities  Variations from normal wave length, height, and depth can indicated health problems