Cardiovascular Physiology Part 2 Flashcards
Why is the rate of action potential propagation slow in cardiac muscle?
Because of gap junctions and the small diameter of the fibers.
Why is the rate of action potential propagation faster in skeletal muscle?
Because of the large diameter of the fibers.
What is the main source of calcium release in cardiac muscle?
Calcium-induced calcium release (CICR).
Describe the process of calcium release in cardiac muscle.
Movement of extracellular Ca²⁺ through the plasma membrane and T tubules into the sarcoplasm stimulates the release of Ca²⁺ from the sarcoplasmic reticulum.
What triggers calcium release from the sarcoplasmic reticulum in cardiac muscle?
Action potential in the T-tubule.
List the phases of the action potential in cardiac muscle.
*Rapid Depolarization
* Plateau phase
* Repolarization
What causes the rapid depolarization phase of the cardiac action potential?
Na⁺ entry.
What causes the plateau phase of the cardiac action potential ?
Ca²⁺ entry.
What causes the repolarization phase of the cardiac action potential?
K⁺ entry (Note: This should likely be K⁺ exit or increased K⁺ permeability leading to efflux.
What is the ionic basis of the rising phase of the action potential in myocardial fibers?
Due to the opening of fast Na⁺ channels.
What ionic events occur during the plateau phase of the action potential in myocardial fibers?
*Closure of Na⁺ channels
* Opening of Ca²⁺ channels
* Slight increase in K⁺ permeability
What is a significant consequence of the plateau phase in cardiac muscle?
Prevents summation and thus tetanus of cardiac muscle.
What ionic event is key to the repolarization phase of the action potential in myocardial fibers?
Ca²⁺ channels closed. Increased K⁺ permeability (leading to K⁺ efflux).
List the components of the conducting system of the heart
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Atrioventricular (AV) bundle (Bundle of His)
- Left and right bundle branches
- Purkinje fibers
What is another name for the SA node and what type of cells does it consist of?
Also called the pacemaker
Consists of specialized cardiac muscle cells (autorhythmic tissues).
What is the function of the SA node?
Generates spontaneous action potentials.
How do action potentials generated in the SA node travel through the atria?
Pass through the atrial muscles.
How is action potential conduction through the AV node different from other parts of the heart? What is the significance of this?
Action potentials are conducted more slowly here than in other parts. This ensures the ventricles receive the signal to contract after the atria have contracted.
How does the AV bundle transmit action potentials to the ventricles?
Passes through a hole in the cardiac skeleton to reach the interventricular septum.
Where do the right and left bundle branches extend?
Extend beneath the endocardium to the apices of the right and left ventricles.
Describe the structure of Purkinje fibers.
Large diameter cardiac muscle cells with few myofibrils. Many gap junctions.
What is the function of Purkinje fibers?
Conduct action potentials to ventricular muscle cells (myocardium).
List the characteristics of autorhythmic cells.
Initiate action potentials.
* Have unstable resting potentials called pacemaker potentials.
* Use calcium influx (rather than sodium) for the rising phase of the action potential.
What is unique about the resting membrane potential of the SA node?
The SA node has no stable resting membrane potential.
