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Questions and Answers
What primarily determines the resting membrane potential of cardiac cells?
What is the role of the Na+-K+ ATPase in cardiac cells?
Which mechanism leads to depolarization of cardiac cells?
What is a major effect of changes in conductance to an ion across the membrane?
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How is the membrane potential changed by an electrochemical gradient?
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What characterizes Phase 0 of the action potential in cardiac conducting cells?
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Which phase in the action potential of SA nodal cells directly contributes to the automaticity of these cells?
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What occurs during Phase 3 of the action potential in SA nodal cells?
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Which statement correctly describes the resting membrane potential of SA nodal cells?
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What ion channel mechanisms contribute to the pacemaker potential in SA nodal cells?
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Study Notes
Autonomic Nervous System and Cardiac Function
- Autonomic nervous system modulates heart rate, conduction velocity, and excitability.
- Electrocardiogram (ECG) is used to assess cardiac electrical activity.
Cardiac Action Potentials
- Cardiac action potentials share principles with those in nerve, skeletal, and smooth muscle cells.
- Membrane potential of cardiac cells is influenced by ion conductances and concentration gradients.
Ion Dynamics
- When the membrane is permeable to an ion, it moves down its electrochemical gradient, impacting membrane potential.
- Resting membrane potential is primarily dictated by potassium ions (K+), with high conductance to K+ closest to its equilibrium potential.
- Na+ -K+ ATPase maintains Na+ and K+ concentration gradients across the membrane, with a minor electrogenic effect.
Changes in Membrane Potential
- Membrane potential changes from ionic flow into or out of the cell; inward current leads to depolarization, while outward current results in repolarization.
- Changes in membrane potential can occur due to altered electrochemical gradients or changes in conductance of ions.
Conducting Cells and Pacemaker Potential
- SA nodal cells experience slow depolarization, creating a pacemaker potential, leading to action potential generation.
- Three ion channel mechanisms contribute to the pacemaker potential.
Phases of Action Potentials in Conducting Cells
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Phase 0 (Depolarization)
- Enhanced calcium conductance and inward Ca2+ current occur primarily through L-type Ca2+ channels.
- Phases 1 and 2 are absent in SA node action potentials.
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Phase 3 (Repolarization)
- Increased potassium conductance causes an outward K+ current and membrane repolarization.
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Phase 4 (Spontaneous Depolarization)
- Represents the majority of SA node action potential, with no true resting potential leading to slow depolarization.
- Threshold potential is where inward current exceeds outward current, triggering the action potential.
Cardiac Muscle Cell Types
- Two main cell types in the heart:
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Contractile Cells
- Majority of atrial and ventricular tissue, responsible for contraction and force generation.
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Conducting Cells
- Includes SA node, AV node, bundle of His, and Purkinje system.
- Specialized for spontaneous action potential generation, though this is usually suppressed except in the SA node.
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Contractile Cells
Key Differences Between Cell Types
- SA node has automaticity, meaning it generates action potentials without neural influence.
- It displays an unstable resting membrane potential and lacks a sustained plateau phase typical of contractile cells.
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Description
This quiz explores the interplay between the autonomic nervous system and cardiac action potentials, focusing on heart rate, conduction velocity, and excitability. It covers relevant concepts that relate to action potentials in nerve, skeletal muscle, and smooth muscle. Test your understanding of these vital physiological processes.
