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Questions and Answers
What primarily affects the resting membrane potential?
What primarily affects the resting membrane potential?
Which of the following best describes non-pacemaker cells?
Which of the following best describes non-pacemaker cells?
What is a key feature of pacemaker action potentials?
What is a key feature of pacemaker action potentials?
What role do ion transport pumps play in the heart?
What role do ion transport pumps play in the heart?
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What distinguishes cardiac action potentials from those in skeletal muscle and nerve cells?
What distinguishes cardiac action potentials from those in skeletal muscle and nerve cells?
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How does the autonomic nervous system influence cardiac activity?
How does the autonomic nervous system influence cardiac activity?
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What type of conduction block is characterized by a complete dissociation between atrial and ventricular depolarizations?
What type of conduction block is characterized by a complete dissociation between atrial and ventricular depolarizations?
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Which abnormality results in ventricular rhythms being generated by distal pacemaker sites with lower intrinsic rates than the SA node?
Which abnormality results in ventricular rhythms being generated by distal pacemaker sites with lower intrinsic rates than the SA node?
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In the context of cardiac tissue, which condition can cause a wide QRS complex?
In the context of cardiac tissue, which condition can cause a wide QRS complex?
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Which of the following conditions requires partial depolarization of a conduction pathway and unidirectional block to occur?
Which of the following conditions requires partial depolarization of a conduction pathway and unidirectional block to occur?
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What effect does sympathetic activation have on AV node conduction velocity?
What effect does sympathetic activation have on AV node conduction velocity?
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An individual experiencing junctional rhythms due to AV block would likely have a heart rate in which range?
An individual experiencing junctional rhythms due to AV block would likely have a heart rate in which range?
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What primarily initiates spontaneous depolarization in pacemaker action potentials?
What primarily initiates spontaneous depolarization in pacemaker action potentials?
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Which ion transport mechanism is associated with negative chronotropy, decreasing heart rate?
Which ion transport mechanism is associated with negative chronotropy, decreasing heart rate?
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During which phase of a non-pacemaker cardiac action potential does rapid depolarization primarily occur?
During which phase of a non-pacemaker cardiac action potential does rapid depolarization primarily occur?
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What effect does sympathetic activation have on nodal action potentials?
What effect does sympathetic activation have on nodal action potentials?
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Which channel contributes primarily to the late phase 3 repolarization of cardiac action potentials?
Which channel contributes primarily to the late phase 3 repolarization of cardiac action potentials?
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What happens to the pacemaker potential during sympathetic activation?
What happens to the pacemaker potential during sympathetic activation?
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What is the effect of hypoxia on heart rate?
What is the effect of hypoxia on heart rate?
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In cardiac action potentials, what is primarily responsible for the plateau phase?
In cardiac action potentials, what is primarily responsible for the plateau phase?
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What is the primary role of the sinoatrial node in the heart?
What is the primary role of the sinoatrial node in the heart?
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Which part of the conduction system is responsible for the slowest conduction?
Which part of the conduction system is responsible for the slowest conduction?
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What effect does sympathetic activation have on conduction velocity?
What effect does sympathetic activation have on conduction velocity?
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Which ion channel blockade decreases conduction velocity in AV node cells?
Which ion channel blockade decreases conduction velocity in AV node cells?
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Which structure in the heart carries the fastest conduction impulses?
Which structure in the heart carries the fastest conduction impulses?
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How do circulating catecholamines influence conduction velocity?
How do circulating catecholamines influence conduction velocity?
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What primarily causes a decrease in the phase 0 slope in AVN cells?
What primarily causes a decrease in the phase 0 slope in AVN cells?
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What is the effect of increased vagal tone on conduction velocity?
What is the effect of increased vagal tone on conduction velocity?
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Which of the following factors may cause abnormal conduction within the heart?
Which of the following factors may cause abnormal conduction within the heart?
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Which mechanism is involved in decreased conduction velocity in non-nodal cells?
Which mechanism is involved in decreased conduction velocity in non-nodal cells?
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Study Notes
Cardiac Electrophysiology Lecture 1
- The lecture covers cardiac electrophysiology, focusing on pacemaker and non-pacemaker action potentials, and electrical conduction in the heart.
- Objectives include explaining how ion changes affect resting membrane potential, describing the electrophysiological basis for action potentials, identifying normal conduction pathways, and describing autonomic nerve effects.
- Learning resources include videos, a textbook chapter, and a journal article, all available from MU resources.
Cardiac Action Potentials
- Cardiac action potentials differ significantly from nerve and muscle action potentials, primarily due to their prolonged duration.
- Cardiac action potentials are not initiated by nerves and neurotransmitters, but some cardiac cells exhibit spontaneous pacemaker activity.
Non-Pacemaker vs. Pacemaker Action Potentials
- Non-pacemaker cells, like atrial and ventricular myocytes and Purkinje fibers, have a true resting potential and exhibit rapid depolarization with a plateau phase followed by repolarization.
- Pacemaker cells, including sinoatrial and atrioventricular nodes, lack a true resting potential and demonstrate spontaneous depolarization and repolarization.
Membrane Potential Generation
- Ion concentration gradients (Na+, Ca++, and K+) and ion conductances (Goldman-Hodgkin-Katz equation) are essential for generating membrane potentials in the heart.
- Electrogenic ion transport (e.g., Na+/K+-ATPase) maintains these gradients.
- Time-dependent changes in ion conductances through gated ion channels cause depolarization and repolarization
Cardiac Ion Channels
- Several ion channels (e.g., sodium, potassium, calcium) are crucial for cardiac action potentials, each with distinct activation and inactivation patterns.
Pacemaker Action Potentials (Slow-response APs)
- Pacemaker potentials, primarily driven by "funny" current (If), initiate spontaneous depolarization.
- Calcium and potassium currents also contribute to depolarization and repolarization.
- The action potential cycle is distinct with a particular emphasis on phases 0, 3, and 4.
- The effective refractory period (ERP) spans phases 0-3.
Pacemaker Cell Locations
- Pacemaker cells are found in the sinoatrial (SA) node (60-100 bpm), the atrioventricular (AV) node (40-60 bpm), and Purkinje fibers (30-40 bpm).
SA Nodal Firing Rate Regulation
- Sympathetic and parasympathetic nervous systems regulate the SA nodal firing rate.
- Sympathetic activation increases the rate (positive chronotropy) via β₁-adrenoceptors.
- Parasympathetic activation decreases the rate (negative chronotropy) via muscarinic receptors.
Autonomic Regulation of Nodal Action Potentials
- Sympathetic activation shortens the time to reach threshold, increases phase 4 slope, and reduces AP duration.
- Vagal activation increases the time to reach threshold, decreases phase 4 slope, and increases AP duration.
Influences on Pacemaker Activity
- Hormones (thyroxine, catecholamines), potassium ions, ischemia/hypoxia, and drugs also affect pacemaker activity.
Non-Pacemaker Action Potentials (Fast-response APs)
- These action potentials involve rapid depolarization, followed by repolarization phases (1-3) that differ depending on their location.
- The action potential is determined by the activation and inactivation of sodium and potassium channels.
- The duration of the action potential is shorter than for the pacemaker action potential.
Conduction of Action Potentials
- Action potentials are conducted from cell to cell via gap junctions to create a functional syncytium.
- Specialized conduction pathways, such as the internodal tracts, bundle of His, bundle branches, and Purkinje fibers, ensure rapid and coordinated impulse spread through the heart.
- The propagation speed varies along these pathways to ensure coordinated ventricular contraction.
Conduction Block and Ectopic Foci
- Conduction blocks can arise from various functional or anatomic abnormalities, e.g., ischemic injury or congenital abnormalities.
- Ectopic foci generate abnormal electrical signals outside the normal conduction pathway, leading to abnormal depolarization patterns.
- Reentry circuits result from partial depolarization of a conduction pathway, unidirectional conduction block, and critical timing.
- Autonomic function changes can affect conduction velocity and influence reentry initiation and resolution.
AV Block
- AV block results in delayed or obstructed conduction from the atria to the ventricles, leading to distinct degrees of AV block (1°, 2°, and 3°).
- AV block causes ventricular rhythm abnormalities like bradycardia.
- Distal sites like the bundle branch and Purkinje fibers can assume the pacemaker role, but their inherent rate is lower than that of the SA node.
Abnormal Conduction
- Various abnormalities (e.g., reentry, ectopic foci) disrupts or changes the timing and order of cardiac muscle cell depolarization, leading to irregular heart rhythms.
Summary
- Cardiac electrical activity is finely controlled and coordinated, influenced by autonomic input, ion concentration gradients, and specialized conduction pathways.
- Disruptions to this system can lead to various cardiac arrhythmias, highlighting the importance of understanding cardiac electrophysiology.
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Description
This quiz covers the fundamentals of cardiac electrophysiology, focusing on pacemaker and non-pacemaker action potentials as well as electrical conduction in the heart. Key objectives include understanding ion changes, normal conduction pathways, and the influence of autonomic nerves on heart activity. Suitable for those studying cardiac physiology.
