Cardiovascular Physiology 9 Flashcards
What are the two types of action potential in the heart?
- Fast response action potential
* Slow response action potential
Where are fast response action potential found?
- Contractile myocytes in the atrial and ventricular myocardium
- Myocytes part of the heart’s conduction system (bundle of His, left and right bundle branches, purkinje fibers)
Where are slow response action potentials found?
Sinoatrial node and the atrioventricular node
What do the terms fast and slow refer to in the two types of action potential of the heart?
How quickly the membrane potential changes during the depolarization phase of the action potential
What is the rate of depolarization in a fast action potential?
Fast
What is the rate of depolarization in a slow action potential?
Slower rate of depolarization where the membrane potential takes more time to reach the new potential
Why do the two types of heart action potentials have different rates of depolarization?
The different combinations of ions and ion channels in the depolarization phase
What are the important ions in the cardiac cells?
Sodium, Potassium and Calcium
What is the concentration of potassium inside and outside the cardiac cell?
There is a high concentration of potassium inside and a low concentration of potassium outside
What is the concentration of sodium and calcium inside and outside of myocytes?
Sodium and calcium have high concentrations outside the cell and low concentrations inside the cell
What are the phases of the Slow Action Potential?
- Pacemaker potential
- Depolarization
- Repolarization
What is the resting potential like in a slow action potential?
Slow action potentials do not have a steady but instead undergo a slow depolarization to threshold
What is the Pacemaker potential of a slow action potential?
The gradual increase of membrane potential
What allows the muscles in the heart to generate action potentials without any external influences?
The slow depolarization of membrane potential
What are the different phases of the slow action potential brought about by?
The changes in the permeability of the membrane to various ions
How does potassium contribute to the pacemaker potential in slow action potentials?
During the pacemaker potential there is a progressive reduction in potassium permeability
What is the reduction in potassium permeability in the slow action potential caused by?
The closing of the potassium channels due to the return of the membrane to the negative potential
When do F-type channels in slow action potentials open?
At negative potentials
What do the F-type channels conduct in the slow action potentials?
Mainly inward sodium current, but they are non specific
What do T-type channels do in the pacemaker potential of slow action potential?
Allow calcium into the cell bringing the channel to threshold
What are the three channels involved in the pacemaker potential?
- K+ channels
- F-type channels
- T-type channels
What is depolarization in a Slow action potential brought about by?
L-type channels that allow an influx of calcium
What do L-type channels do in a slow action potential?
Allow an influx of calcium during depolarization
What causes the repolarization of the slow action potentials?
The closing of L-type channels and the opening of potassium channels allowing potassium to leave the cell
What channels are involved in depolarization of slow action potentials and what do the channels do?
L-type channels that allow calcium into the cell slowly
What channels are involved in Repolarization in slow action potentials and what do those channels do?
Potassium channels that allow potassium to leave the cell
What are responsible for the depolarization phase of the slow action potential?
Calcium currents
How does calcium affect the rate of slow action potentials?
Calcium move through the channel more slowing resulting in a slow increase in membrane potential
What occurs with the channels during the pacemaker phase of slow action potentials?
- Potassium channels close when the cell is at a negative membrane potential stopping potassium flow leaving the cell
- F-type channels open allows sodium to enter the cell
- T-type channels open allowing calcium to enter the cell depolarizing the membrane
What occurs during the depolarization phase of a slow action potential?
•L-type channels open allowing calcium to slowly enter the cell moving down its concentration gradient
What occurs during the repolarization phase of a slow action potential?
- Potassium channels open allowing potassium to leave the cell
- L-type calcium channels close inhibiting calcium to enter the cell
What is the difference in pacemaker potential of the AV and SA node?
The pacemaker potential in the AV node rises more slowly to threshold than the SA node
