Cardiac Conduction Pathway
Cardiac Conduction
Conduction Pathway:
1. SINOATRIAL NODE
The sinoatrial (SA) node is located in the upper wall of the right atrium, near the opening of the superior vena cava.
Pacemaker: fastest rate of autorhythmicity, therefore, sets heart rate; the action potential originates here.
2. ATRIOVENTRICULAR NODE
The AV node is located at the base of right atrium, adjacent to septum.
It is the only electrical communication between the atria and the ventricles, and that it delays impulses to facilitate peak cardiac output.
AV nodal delay: delays impulses, maximizes stroke volume, increases cardiac output.
3. BUNDLE OF HIS
Originates at AV node, splits at interventricular septum into left and right bundle branches.
4. PURKINJE FIBERS
Spread upward through ventricular walls. Ventricles contract when these fibers are activated.
Cardiac muscle cell action potential
PHASE 0: DEPOLARIZATION
The initial rise of the curve.
Sodium moves rapidly into cell; calcium moves slowly into the cell.
PHASE 1
Peak of curve.
Voltage-gated sodium channels close.
PHASE 2: PLATEAU PHASE
Curve plateaus.
Potassium moves rapidly out of cell, while calcium moves slowly into the cell.
Calcium enters from both the extracellular space and sarcoplasmic reticulum, and is the cause of the plateau.
PHASE 3: RAPID REPOLARIZATION
Curve declines.
Calcium channels close and potassium moves rapidly out of cell.
Potassium and sodium ion positions in regards to the sarcolemma are reversed.
PHASE 4: RESTING POTENTIAL
Low curve.
The resting potential is maintained by leaky potassium channels.
The sarcolemma is impermeable to sodium during this period.
- * Long absolute Refractor period: