14 Electrical activity of the heart Flashcards
State the electrical conduction pathway of the heart from the SA node.
SA node > both atria > AV node > bundle of His > Purkinje fibers
How long is an action potential in SA node last?
150 ms
In SA node, what is the sequence of phases during a pacemaker potential?
4 > 0 > 3
What happens in phase 4 of SA node potential? (What type(s) of current)
- Inward Na+ current and T-type Ca2+ current
- Rate of phase 4 determines heart rate
What ion is involved in phase 0 of SA node potential? What is the effect?
inward Ca2+ current (L-type)
Depolarization
What ion is involved in phase 3 of SA node potential? What is the effect?
Outward K+ current
Repolarization
Are there any phase 2 (plateau) in pacemaker potentials?
No
What is the duration of action potential in atria and in ventricles respectively? Why is there a difference?
Atria: 150 ms
Ventricles: 250ms
long refractory period in ventricles due to Na+ channel inactivation that prevents summation of multiple cardiac contractions
What are the phases involved in action potential in atria and the ventricle?
0,1,2,3,4
What ion is involved in phase 0 of atrial/ventricular action potential? What is the effect?
upstroke
- inward Na+ current
What ion is involved in phase 1 of atrial/ventricular action potential? What is the effect?
initial repolarization
- transient outward K+ current
What ion is involved in phase 2 of atrial/ventricular action potential? What is the effect?
plateau - 0 net current
- inward Ca2+ current and outward K+ current
What ion is involved in phase 3 of atrial/ventricular action potential? What is the effect?
Repolarization
- outward K+ current
What ion is involved in phase 4 of atrial/ventricular action potential? What is the effect?
Resting membrane potential
There is an AV delay of _______ ms to allow __________.
100;
sufficient ventricular filling time
_______ form part of intercalated discs and join ends of cardiomyocytes. There is very low resistance among them to allow fast conduction of action potentials.
Gap junctions
SA nodal action potentials normally occur between ___ to ____ beats per minute
60-100
Which of the following are abnormal situations- ectopic pacemakers?
A. SA nodal firing is too slow
B. SA node is damaged or activity inhibited
C. latent pacemakers fire at a greater rate than SA node
D.conduction pathway is damaged, e.g. different types of heart blocks
all of the above
In sympathetic systems, which 2 NT will activate the b1 receptors in the heart to increase contractility and heart rate?
Adrenaline and noradrenaline
What is released in parasympathetic system? What receptor are activated?
Acetylcholine
M2 receptors in SA node, AV node and atria
(NOT in ventricles)
How does activating M2 receptors in parasympathetic stimulation cause a negative chronotropic effect?
M2 receptors is coupled to Gi protein.
AC inhibition, thus less cAMP,
slower phase 4
increased threshold of action potential
How does activating b1 receptors in sympathetic stimulation cause a positive chronotropic effect - increased conduction velocity?
b1 is coupled to Gs protein
increase AC increase cAMP > PKA
thus increase in Ca2+ for faster upstroke of action potential
