13- Cardiac Action Potentials & Conduction Flashcards
What is the order of the cardiac action potential, generally?
SA Node AV Node Bundle of His Right/Left Bundle Branch (Left subdivides further) Purkinje Fibers
***All of these can have pacemaker properties under the right conditions!
What is usually considered the pacemaker of the heart?
SA Node
During which phase of an acton potential is the membrane potential closest to the K+ equilibrium potential throughout that phase?
A) Phase 0 B) Phase 1 C) Phase 2 D) Phase 3 E) Phase 4
E) Phase 4
What is the major cause of depolarization (phase 0) of a neuronal action potential?
A) Decreased K+ conductance B) Increased Ca2+ conductance C) Increased Na+ conductance D) Increased K+ conductance E) Decreased Ca2+ conductance
C) Increased Na+ conductance
Which of the following is the major contributor to repolarization of an excitable cell’s action potential?
A) Opening of voltage-gated K+ channels B) Opening of voltage-gated Na+ channels C) Closure of voltage-gated K+ channels D) Opening of voltage-gated Ca2+ channels E) Closure of Na+/K+ ATPase
A) Opening of voltage-gated K+ channels
Conduction velocity of the heart gets faster as the cells/fiber diameter (INCREASES/DECREASES).
Increases
Rank the following components of the heart from fastest to slowest based on their conduction velocity:
A) AV Node
B) Purkinje Fibers
C) Atrial and Ventricular Myocytes
B) Purkinje Fibers
C) Atrial and Ventricular Myocytes
A) AV Node
These can also create action potentials and beat spontaneously, but they are much slower than the SA Node.
AV Node (slower) Purkinje Fibers (slowest)
This is the term for maintaining order for the pacemaker of the heart. The SA Node will remove pacemaker activities from the AV Node or Purkinje Fibers because it fires the fastest, making sure it maintains order for the heart.
Overdrive Suppression
Which Atrium will contract first?
Right Atrium then Left Atrium
The (EPICARDIUM/ENDOCARDIUM) will contract prior to the (EPICARDIUM/ENDOCARDIUM).
Endocardium
Epicardium
The (LEFT/RIGHT) Ventricle epicardium will contract before the (LEFT/RIGHT) Ventricle epicardium.
Right
Left
Describe the Na+ current (I-Na).
Activated when threshold is reached, and is the opening of the voltage-gated Na+ channel.
Phase 0 and 1
Describe the Transient Outward K+ current (I-to).
Activated when the cell depolarizes, and there is very rapid depolarization via the opening of K+ channels.
Phase 1
Describe the Calcium current (I-Ca).
Activated when the cell depolarizes, (L-type Ca Channel) slow to open and remains open for a determined amount of time then closes causing Phase 3.
Phase 2 and a little of Phase 3
Describe the Inward Rectifying K+ current (I-K1).
Activated when the cell depolarizes, slow to closed and remains closed for a determined amount of time then opens helping with Phase 3. Still voltage-sensing.
Phase 2 and 3
Describe the Rapid and Slow K+ current (I-Kr, I-Ks).
Activated at the peak, and is the opening of the voltage-gated K+ channels either rapid or slow. Contribute to Phase 3 repolarization.
Phase 3
Describe the K+ current for the leak channels (I-K).
Activated all the time (remain open), these are the K+ leak channels.
Phase 4
Describe the Na+ funny current (I-Naf).
Activated at threshold, contribute to the rise in membrane potential in the SA and AV Node. Close at threshold but open during repolarization to bring the slow depolarization from RMP.
Phase 4
Phase _____ in the SA Node and AV Node resting membrane potential gradually depolarizes until it reaches threshold, then it fires (slower than other regions). The intrinsic, spontaneous depolarization makes this the pacemaker.
Phase 4
Phase ______ in the SA Node and AV Node is the opening of voltage-gated Ca2+ channels rather than voltage-gated Na+ channels, and the closure of voltage-gated K+ channels (rectifiers).
Phase 0
Phase ______ in the SA Node and AV Node is the reversal of Phase 0. There is a closure of voltage-gated Ca2+ channels and opening of voltage-gated K+ channels (both rectifiers and traditional).
Phase 3
The SA Node and AV Node will naturally depolarize to reach threshold without electrical stimulation. The AV Node does this but slower. _________ _________ dictates that stimulation of AV Node by the SA Node will trigger AV Node to generate an action potential prior to when it would do so on its own. This also prevents ________ ________ and ________ _________ from firing spontaneously as their rate of Phase 4 is even slower.
Overdrive Suppression
Bundle Branches
Purkinje Fibers
These are periods when AP cannot be generated or are generally more difficult to generate. They are longer in cardiac cells and help to prevent arrhythmias.
Refractory Periods
During this refractory period, the Na+ inactivation gates are closed and cannot be activated again no matter what.
Absolute Refractory Period
***This is from Phase 0 to about middle Phase 3
During this refractory period, a greater stimulus will create another AP, but it won’t look and feel like it should (abnormal conduction).
Relative Refractory Period
***Middle to end of Phase 3
This type of refractory period is new, and the cell is more excitable than normal and easier to generate an AP. It may have abnormal conduction.
Supranormal Period
***At the very end of Phase 3 right before Phase 4 is reached
It stimulated during a Relative Refractory Period or Supranormal Period, the conduction of the AP will be (STRONGER/WEAKER).
Weaker
***The AP is stronger in Supranormal than Relative Refractory
This is the term for effect changes in heart rate. It is the slope of depolarization in Phase 4 at the SA Node.
Chronotropic
A positive chronotropic effect is a (FASTER/SLOWER) heart rate. A negative chronotropic effect is a (FASTER/SLOWER) heart rate.
Faster
Slower
This is the term for effect speed of conduction (conduction velocity). It is the slope of Phase 0. Basically, how quickly the heart contracts.
Dromotropic
This is the term for effect strength of muscular contraction.
Inotropic
This is the term for effect rate of muscular relaxation.
Lusitropic
Parasympathetic stimulus is carried by the _______ N.
Vagus N.
Parasympathetics go to the SA Node and AV Node, but is insignificant to the Ventricular myocytes. The NT released is __________ and the receptors are __________.
ACh
Muscarinic (M2/M3)
***Remember, Parasympathetics slow down HR
Parasympathetics have (POSITIVE/NEGATIVE) chronotropic effects due to slower opening of funny sodium channels during Phase 4, and hyperpolarization of the SA Node by increasing outward K+ current via special K+ channels (K+ ACh channel).
Negative
Parasympathetics have (POSITIVE/NEGATIVE) dromotropic effects due to reduced inward Ca2+ current and an increasing outward K+ current via special K+ channels (K+ ACh channel).
Negative
Sympathetics go to the SA Node, AV Node, and Ventricular myocytes but not _________ myocytes. The NT is _________ and the receptors are __________.
Atrial
Norepinephrine
B1-Adrenergic
Sympathetics have (POSITIVE/NEGATIVE) chronotropic effects due to more rapid opening of funny sodium channels during Phase 4.
Positive
Sympathetics have (POSITIVE/NEGATIVE) dromotropic effects due to increased inward Ca2+ current.
Positive
Sympathetics also cause a (POSITIVE/NEGATIVE) inotropic or lusitropic influence.
Positive
***Remember, Parasympathetics have no inotropic or lusitropic influence.
