Flashcards in Cardiac Ion Channels & Action Potentials Deck (40):
T or F: Electrical activity propagates within myocardium AND via specialized conductive pathways
What cardiac structure serves as the main control for HR?
pacemaker cells in the sinoatrial node (SA node).
-fire intrinsically at ~100/min.
-Rate modulated by ANS.
What slows down the intrinsic HR of the SA node?
Parasympathetic tone slows rate to 60-80/min.
T of F: AV node is also capable of spontaneous activity
What is overdrive suppression?
Describes how the AV node is driven by action potentials originating in the SA node since their firing frequency is less than the SA node.
What are ectopic pacemakers?
Self firing cells that (or others, especially cells in damaged regions of the myocardium) can take over initiation of the heartbeat Under abnormal circumstances
How does cell-to-cell conduction take place?
How is the direction of electricl propagation controlled?
by gap junction position and by connective tissue “insulation” (e.g., between the atria and ventricles).
T of F: The AV node is the only place where action potentials can propagate from the SA node to the ventricles.
Which structures are characterized as having a fast action potential?
-Atrial and ventricular muscle
Which structures are characterized as having a slow action potential?
SA & AV nodes
Direction of current flow depends on what?
-membrane potential (Vm) and
-ion gradient (Nernst Potential, Eion)
T or F: If Vm
T or F: If Vm>Eion, current flows out of cell
What causes depolarization?
Current flowing into cell causes depolarization
What causes hyperpolarization?
Current flowing out of cell causes hyperpolarization
T or F: ion channels serve as gates; open upon depolarization and close upon repolarization
T of F: Current is constant with voltage
T of F: If we keep the voltage positive inactivation gate closes with time
What is the characteristic subunit in cardiac sodium channels?
NaV1.5 , cardiac Na channels show Voltage-dependent inactivation
What are the types of Ca++ channels in the heart?
L & T types. Also, Ryanodine Receptors (intracellular- SR)