Conduction system
What part of the conduction system directly activates the ventricular myocardium?
Purkinje fibers
The natural pacemaker setting the rhythm of the heart
SA node
Cutting the vagus nerve results in
spike in heart rate!
Which ion is responsible for the rapid depolarization phase of the SA node action potential?
Calcium
What is a first-degree AV block
delay in impulse conduction through the AV node
Which structure conducts the impulse from the AV node to the left and right ventricles?
Bundle of His
Delays the cardiac impulse
AV node
Which neurotransmitter is released by the parasympathetic nervous system to slow down the heart rate by acting on the SA node?
Acetylcholine
What ion channel opens during repolarization?
Potassium
What is the significance of the ST-segment elevation on an ECG, and what does it typically indicate?
ST-segment elevation indicates acute myocardial injury, commonly myocardial infarction.
Why does the cardiac impulse need to travel through the Purkinje fibers?
To ensure rapid and coordinated contraction of BOTH ventricles
Where is the SA node located in the heart?
upper wall of the right atrium near the opening of the superior vena cava
Name the two types of receptors that regulate HR (inc/dec) through sympathetic and parasympathetic innervation
Beta-1 adrenergic (sympathetic stimulation)
Muscuranic M2 receptors (parasympathetic)
What distinguishes the SA node action potential from that of ventricular myocytes in terms of ion channels?
SA: Ca
Ventricles: Na
effect of heart block on ECG
Prolonged PR interval
Refractory period prevents tetanus in cardiac muscle by
Preventing very fast, continuous stimulation allowing it to fill and relax
What is the intrinsic firing rate of Purkinje fibers when they function as pacemakers?
15-40 bpm
Describe the role of chemoreceptors in regulating heart rate during hypercapnia
stimulate the sympathetic nervous system to increase heart rate, improving oxygen delivery to tissues
During which phase of the SA node action potential does the “funny current” (If) occur?
Phase 4 (spontaneous depolarization)
How do calcium channel blockers affect the cardiac conduction system, particularly the SA and AV nodes?
they slow conduction through the AV node and decrease heart rate by reducing calcium influx
How would a blockage in the left bundle branch affect the propagation of the cardiac impulse?
causes delayed depolarization of the left ventricle, leading to abnormal heart rhythms and inefficient pumping
How does hyperkalemia (high potassium) affect the pacemaker activity in the SA node?
slows down or suppresses pacemaker activity, potentially leading to bradycardia or cardiac arrest
Which area of the brain contains the cardiovascular center that regulates heart rate?
Medulla Oblongata
How does the slope of Phase 4 (pacemaker potential) in the SA node influence heart rate, and which factors can modulate this slope?
steeper slope increases heart rate by reaching the threshold potential faster, and factors like sympathetic stimulation (norepinephrine) or parasympathetic inhibition (acetylcholine) can modulate this slope.
What is the clinical presentation of Sick Sinus Syndrome, and how does it affect the SA node?
Dysfunction of the SA node, leading to alternating episodes of bradycardia and tachycardia