1. February 26, 2016
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
Bundle of His divides into the right bundle branch and the left bundle branch
Purkinje fibers carry the impulses to the muscle cells

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