Cardiac Action Potentials & Conduction Flashcards
Delineate the conduction system of the heart.
SA node AV node AV bundle R and L bundle branches subendocardial branches
List the cardiac cell areas that have intrinsic pacemaker abilities in order from most frequent action potential to least frequent.
SA node
AV node
subendocardial branches
What is a problem with the subendocardial fibers if only they were left to generate action potentials for the heart’s contraction?
- subendocardial fibers’ action potentials are not synchronized
- cardiac muscle ctx would be chaotic
True or False: fibers with a larger diameter deliver signals more quickly
True
What happens in Phase 0 of ventricular and atrial action potentials?
rapid depolarization
-voltage-gated Na+ channels open
What happens in Phase 4 of SA node action potential?
gradual depolarization
What ionic conditions are responsible for the long action potential (dragging out of Phase 2) in cardiac muscle?
+calcium coming into the cell
+potassium is prevented from leaving the cell (IK1)
– voltage-gated K+ channels let K+ out of cell
–K+ leak channels let K+ out of cell
— combination of all this interplay
What happens during Phase 1 of ventricular action potentials?
-transient outward K+ current
–keeps the Na+ channels from overshooting
What happens during Phase 3 of ventricular action potentials?
-repolarization of the cell
- -increased activity of voltage-gated K+ channels
- -inward rectifier channels open to let K+ out (IK1)
Can an action potential fire during the Absolute Refractory Period?
no
Can an action potential fire during the Relative Refractory Period?
yes, but it requires a greater stimulus and/or will have abnormal conduction
What is the Supranormal Period?
-when the cell is more excitable than normal and it’s easier to generate an action potential, but may have abnormal conduction
What are chronotropic changes in reference to?
heart rate
What are dromotropic changes in reference to?
speed of conduction
What are inotropic changes in reference to?
strength of ctx
What are lusitropic changes in reference to?
rate of relaxation
What supplies parasympathetic innervation to the heart?
cardiac branches of the vagus N.
True or False: parasympathetic innervation to the heart goes only to the SA and AV nodes, not to the ventricles
True
What is the neurotransmitter and receptor combination used in parasympathetic innervation to the heart?
Ach muscarinic receptors (M2 and M3)
What is the negative chronotropic effect caused by parasympathetic innervation of the heart?
- slower opening of funny Na+ channels during Phase 4
- increase in outward K+ current via K(ach) channels
What is the negative dromotropic effect caused by parasympathetic innervation of the heart?
- reduced inward calcium current
- increased outward K+ current
- hyperpolarization
What provides sympathetic innervation to the heart?
cardiac splanchnic N.
T1-T5
True or False: sympathetic innervation goes to SA and AV nodes, as well as to the ventricles
True
What is the neurotransmitter and receptor combination for sympathetic innervation to the heart?
norepinephrine
beta-1 adrenergic receptors
What is the positive chronotropic effects caused by sympathetic innervation of the heart?
-more rapid opening of funny Na+ channels during phase 4
What is the positive dromotropic effect caused by sympathetic innervations of the heart?
increased inward calcium current
Does sympathetic innervation has a positive or negative effect on inotropy and lusitropy?
positive
- increased contractility
- increased rate of relaxation
