Cardiac Electrophysiology Flashcards
What is Phase 0 characteristic of in the ventricular myocyte AP?
Rapid Depolarization and Influx of Na+ ions
What is Phase 1 characteristic of in the ventricular myocyte AP?
Early Repolarization through Cl- ion influx and Na+ efflux.
What is Phase 2 Characteristic of in the ventricular myocyte AP?
AKA Plateau phase, and effective refractory period (ERP). K+ channels start repolarizing and SLOW opening Ca2+ channels open and potential plateaus.
What is Phase 3 Characteristic of in the ventricular myoctye AP?
Repolarization: by closing Ca2+ channels and opening up K+ channels.
Which potassium channel is responsible for Phase 1 and remains active until after phase 2?
ito potassium channels.
Which potassium channel is slow activating during phase 2 and begins to dominate once Ca2+ channels close?
ikr potassium channels.
also somewhat responsible for phase 3 hyperpolarization
Which potassium channel is responsible for flux in phase 3 & 4?
ik1 potassium channels.
Which potassium channel is relevant with respect to the regulation of cardiac AP via the parasympathetic nervous system.
ikAch potassium channels. (activated by acethylcholine and is Gi-coupled)
What are the characteristics of the L-Type calcium channels?
They are LONG lasting and SLOW inactivation.
What are the characteristics of the T-Type calcium channels?
They have FAST inactivation and are transient. They are also less abundant.
Which calcium channels are the target for Calcium Channel Blocker drugs?
L-Type Ca2+ channels.
What happens to force of contraction after the Plateau phase contraction is accomplished? (AKA Refractory Period)
The Ventricular myocyte begins to relax and during that period it CANNOT depolarize more and CANNOT bring up another contractile response.
What can happen during the relative refractory period?
The myocyte is relaxing and is partially repolarized and a premature depolarization can happen and cause a weaker contraction. (Premature contraction)
Why is a Premature Contraction possible during the relative refractory period?
- Ca2+ hasnt moved out
- # of Ca2+ channels that can be depolarized is lower
- Less Ca2+ in the cell itself.
True or False. A premature contraction causes a faster heart rate.
True
True or False. If you are experiencing a faster heart rate than normal while exercise it is due to a premature contraction.
False ( After the relative refractory period has passed you can a have a full contraction that is earlier than normal through induced mechanisms (during exercise)
When depolarization occurs where does Ca2+ flow?
It flows into the cytosol of the ventricular myocyte.
What is Calcium Induced Calcium Release?
It is when the Ca2+ flowing into the cytosol attaches to voltage gated Ca2+ channels on the SR and induce the release of stored Ca2+.
Once stored Ca2+ from the SR is released what happens?
Since the Ca2+ level is elevated in the cytosol it interacts with the sarcomere and causes contractions.
What are the 2 ways that cardiac myocytes sequester Ca2+ after contraction?
- Ca2+/ATPase on the SR
2. Ca2+/Na+ exchanger and Na+/K+ ATPase (secondary active transport)
Why is Extracellular Ca2+ important for cardiac myoctyes?
- The SR in cardiac muscle is less developed and does not store enough Ca2+
- T tubules are larger and allow Ca2+ to enter easily
Why is skeletal muscle not affected by extracellular Ca2+ but cardiac muscle is not?
Because skeletal muscle stores enough Ca2+ in the SR and the action potential itself causes the release of Ca2+
Which pacemaker of the heart is located at the top of the right atrium?
The SA node
How is the SA node and AV node connected?
Through Internodal Pathways
