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Electrical Conduction System of the Heart quiz #3

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  • Describe the pathway of an action potential through the cardiac conduction system, listing the main structures involved in order.
    The action potential starts at the sinoatrial (SA) node, spreads through the atria via internodal pathways, reaches the atrioventricular (AV) node (where there is a brief delay), travels down the atrioventricular bundle (bundle of His), splits into right and left bundle branches, and finally spreads through the Purkinje fibers to stimulate ventricular contraction.
  • Explain how the autonomic nervous system modulates heart rate and contractility, specifying the roles of the sympathetic and parasympathetic pathways.
    The sympathetic nervous system increases heart rate and contractility by acting on the SA and AV nodes and heart muscle, while the parasympathetic nervous system decreases heart rate by acting on the SA and AV nodes but does not affect contractility.
  • What is the primary function of the intrinsic cardiac conduction system?
    It initiates and conducts action potentials within the heart, enabling coordinated and regular heartbeats without requiring neural input.
  • Where does the action potential that triggers a heartbeat originate in the heart?
    It originates in the sinoatrial (SA) node, which contains pacemaker cells that depolarize at regular intervals.
  • List the main structures in order that an action potential passes through in the cardiac conduction system.
    The action potential travels from the SA node, through internodal pathways, to the AV node, down the AV bundle (bundle of His), into the right and left bundle branches, and finally through the Purkinje fibers.
  • What is the purpose of the delay at the atrioventricular (AV) node during the cardiac conduction process?
    The AV node delays the action potential for about 100 milliseconds to ensure the atria contract and empty blood into the ventricles before the ventricles contract.
  • How do gap junctions contribute to the coordinated contraction of the heart?
    Gap junctions allow action potentials to rapidly spread from cell to cell, enabling the heart muscle to contract as a unit.
  • What is the role of the Purkinje fibers in the cardiac conduction system?
    Purkinje fibers rapidly distribute the action potential throughout the ventricular walls, triggering coordinated ventricular contraction.
  • How does the sympathetic nervous system affect heart rate and contractility?
    The sympathetic nervous system increases both heart rate and contractility by acting on the SA and AV nodes and the heart muscle.
  • What effect does the parasympathetic nervous system have on the heart, and through which nerve does it act?
    The parasympathetic nervous system decreases heart rate by acting on the SA and AV nodes via the vagus nerve, but it does not affect contractility.
  • Where is the normal pacemaker of the heart located?
    The normal pacemaker of the heart, the sinoatrial (SA) node, is located in the superior right atrial wall, just below the opening of the superior vena cava.
  • What structure acts as the pacemaker of the cardiac conduction system?
    The sinoatrial (SA) node acts as the pacemaker of the cardiac conduction system.
  • Which structure is responsible for initiating the heartbeat in the heart's conduction system?
    The sinoatrial (SA) node is responsible for initiating the heartbeat.
  • What is the normal pacemaker of the heart?
    The normal pacemaker of the heart is the sinoatrial (SA) node.
  • What is the correct sequence of parts that carry cardiac impulses through the heart?
    The correct sequence is: sinoatrial (SA) node → internodal pathways (atrial conducting fibers) → atrioventricular (AV) node → atrioventricular (AV) bundle (bundle of His) → right and left bundle branches → Purkinje fibers (subendocardial conducting network).
  • What is the function of the sinoatrial (SA) node in the heart?
    The SA node initiates action potentials that set the rhythm for the heartbeat, acting as the heart's primary pacemaker.
  • What is autorhythmicity in the heart and which cells are responsible for it?
    Autorhythmicity is the heart's ability to generate its own rhythmic action potentials without external neural input, and it is the responsibility of pacemaker cells, primarily in the SA node.
  • What is the role of pacemaker cells in the heart?
    Pacemaker cells are specialized cardiac cells that depolarize at regular intervals, initiating action potentials that regulate the heart's rhythm.
  • What is considered the natural pacemaker of the heart?
    The sinoatrial (SA) node is considered the natural pacemaker of the heart.
  • Where does the electrical impulse of the heart normally begin?
    The electrical impulse of the heart normally begins at the sinoatrial (SA) node.
  • How does the atrioventricular (AV) node contribute to the heart's conduction system?
    The AV node receives the action potential from the atria, delays it briefly to allow ventricular filling, and then initiates the action potential that triggers ventricular contraction.
  • What is the function of the Purkinje fibers in the cardiac conduction system?
    Purkinje fibers rapidly conduct the action potential throughout the ventricles, ensuring coordinated and efficient ventricular contraction.
  • How does the autonomic nervous system influence heart rate?
    The sympathetic nervous system increases heart rate and contractility, while the parasympathetic nervous system decreases heart rate without affecting contractility.
  • What is the significance of the delay at the atrioventricular (AV) node?
    The delay at the AV node ensures that the atria contract and empty blood into the ventricles before the ventricles contract.
  • What are chronotropic factors and how do they affect the heart?
    Chronotropic factors are extrinsic influences, such as neural input, that change the heart rate by affecting the activity of pacemaker cells.