UNIT 2 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:1. SA Node AV Node

2. Atria Contract

3. (Delay) AV Bundle

4. 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 CyclePhase 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.

(5) Diastole Details1. 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 Details1. Pressure increases in ventricles

- Filled with blood

2. 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) 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.

(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

(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