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?

Electrical Pathways of the Heart

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

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

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

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

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

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

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