15 Questions
What is unique about the plateau phase of the action potential in cardiac contractile cells?
It is the result of prolonged Ca2+ entry
What type of ion channels open at threshold to cause the rapid rising phase of the action potential in cardiac contractile cells?
Fast Na+ channels
Which type of fibers are spread throughout ventricular myocardium and have the fastest conduction speed?
Purkinje fibers
What causes the rapid falling phase of the action potential in cardiac contractile cells?
K+ exit
How do action potentials in cardiac contractile cells differ from those in cardiac autorhythmic cells?
They have a unique plateau phase in contractile cells
What happens if Purkinje fibers are damaged?
An ectopic focus takes over pacemaker activity.
Which type of cells have higher action potential conduction than the SA node?
Contracile cells
What is a characteristic of autorhythmic cells in the heart?
They are capable of generating electrical impulses spontaneously.
What is the result of an ectopic focus driving the heart rate?
The heart is driven more rapidly.
Where are autorhythmic cells typically found in the heart?
In specific sites in the heart, including the SA node and AV node.
What is the origin of the bundle of His?
AV Node
What is the function of the bundle of His?
To conduct electrical impulses from the AV Node to the ventricles
What is the path of the bundle of His after it divides?
It travels down the septum and around the ventricular chambers
What type of cells make up the bundle of His?
Specialized cardiac muscle cells
What is the significance of the bundle of His in the electrical conduction pathway of the heart?
It is the primary pathway for electrical conduction from the AV Node to the ventricles
Study Notes
Heart Conduction System
- Purkinje fibers spread throughout ventricular myocardium and have the fastest conduction speed.
Action Potential of Cardiac Muscle
- The action potential (AP) in cardiac contractile cells differs from that in cardiac autorhythmic cells.
- The rapid rising phase of AP in contractile cells is a result of Na+ entry upon opening of fast Na+ channels at threshold.
- The unique plateau phase results from prolonged Ca2+ entry upon opening of slow Ca2+ channels.
- The rapid falling phase is a result of K+ exit upon opening of K+ channels.
Bundle of His
- A tract of specialized cells originating at the AV node that enters the septum between the ventricles.
- Divides to form the right and left bundle branches that travel down the septum.
- Curves around the apex of the ventricular chambers and travels back towards the atria along the outer walls.
Purkinje Fibers Damage
- If Purkinje fibers are damaged, an abnormal pacemaker takes over.
- The abnormal pacemaker drives the heart at a faster rate than the SA node.
- The heart becomes abnormally excitable, with contractile cells having higher AP conduction than the SA node.
This quiz covers the action potential of cardiac muscle cells, including the rapid rising phase and plateau phase, and how they differ from autorhythmic cells.
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