Anatomy Unit 2: Cardiac Conduction Notes

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:
1. SA Node  AV Node
2. Atria Contract
3. (Delay)  AV Bundle
4. 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
1. 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
1. Pressure increases in ventricles
- Filled with blood
1. 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