UNIT 3 NOTES: Cardiac Conduction System

(1) Conduction System of Heart Conduction System = Heart Beat & Pumping Cardiac Contractions = Unconscious Autonomic Nervous System  decrease or increase heart rate depending on circumstance

(2) Depolarization Path of the Heart Describes the path the nerve impulses travel to make the heart contract and pump blood. The Path: SA Node  AV Node Atria Contract (Delay)  AV Bundle Ventricles Contract (Blood ejected out of arteries, leaving heart)

(3) Nodes & Bundles Sinoatrial Node (SA Node) Right atrium Starts each heart beat & sets rate “Pacemaker” Atrioventricular Node (AV Node) = Left atrium AV Bundle = Bundle Branches (along septum) Purkinje Fibers (along entire muscular wall of heart)

(4) Cardiac Cycle Phase 1- Diastole (Relaxation) Blood passively filling atria Phase 2-Systole (Contraction) Ventricles contract Blood Ejected out of heart

(5) Diastole Details Ventricles relax 2. Semilunar valves closed 3. Ventricular Presure < Atrial Pressure AV valves open Ventricles fill with blood 4. Atria contract and force blood remaining in chambers into ventricles

(6) Systole Details Pressure increases in ventricles AV valves close Filled with blood AV valves close 3. Pressure in ventricles > Arteries leaving heart Semilunar valves open Blood rushes out of ventricles 4. Atria are relaxed and begin to fill back up

(7) Heart Beat You hear something like “lub” “dup” “lub” = closing of AV valves During ventricular systole “dup” = closing of semilunar valves During early diastole You should NOT hear blood flow You’ll hear it if flow is interrupted by blockage

(8) Starling’s Law Starling’s Law of the Heart: Degree of cardiac muscle extension before contraction Increase Extension = Stronger Contraction Degree of Extension  result of percent filling of ventricles