1. UNIT 2 NOTES: Cardiac Conduction System

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

3. (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)

4. (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)

6. (4) Cardiac Cycle Phase 1- Diastole (Relaxation)
Blood passively filling atria.
All valves exiting ventricles closed.
Phase 2-Systole (Contraction)
Ventricles contract and blood ejected out of heart.
All AV valves must be closed.

8. (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

10. (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

12. (7) Cardiac Conduction Summary
Diastole:
Semilunar valves are closed.
AV valves are open.
Blood passively pouring into atria, and down into ventricles.
Only slight contraction of atria at the end to empty atria.
AV valves swing shut when ventricles full.
Systole:
AV valves are closed.
Ventricles contract and pump/eject blood out of heart.
Blood exits out Semilunar Valves (which must open).
Semilunar Valves close back up at end, and AV valves open back up.

13. (8) 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

14. (9) 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