Questions and Answers
What are positive chronotropic effects associated with?
What type of effects do sympathetic stimulations have on heart rate?
How does parasympathetic stimulation affect the SA node's action potential?
What term describes the effects of the autonomic nervous system on conduction velocity in the heart?
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What is the result of sympathetic stimulation on conduction velocity in the AV node?
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Which of the following changes occurs with parasympathetic stimulation?
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What is the primary function of the vagus nerve in relation to heart activity?
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Sympathetic stimulation affects which specific phase of the SA node's action potential?
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Negative chronotropic effects indicate what kind of change in heart rate?
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What occurs to myocardial contractility under sympathetic stimulation?
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Study Notes
Cardiac Muscle Structure and Function
- Cardiac muscle forms an interconnected syncytium, enabling simultaneous action potential transmission among heart cells.
- Two functional syncytiums compose the heart: atrial syncytium (walls of atria) and ventricular syncytium (walls of ventricles).
- Atrial contraction precedes ventricular contraction, optimizing heart pumping efficiency.
Specialized Excitatory and Conductive Fibers
- The system comprises the following components:
- Sinoatrial (SA) node
- Atrial internodal pathways
- Atrioventricular (A-V) node
- A-V bundle (bundle of His)
- Left and right bundle branches of Purkinje fibers
The SA Node
- The SA node acts as the heart's pacemaker, initiating action potentials crucial for rhythm.
- Action potentials propagate through a specific sequence to coordinate heart contractions.
Internodal Pathways and A-V Node
- Action potentials spread from the SA node to both atria and the A-V node.
- The A-V node delays impulse transmission to ventricles, allowing them to fill adequately with blood before contraction.
A-V Bundle
- Also known as the bundle of His, it transmits impulses from the atria to the ventricles.
Cardiac Action Potentials
- Cardiac action potentials share concepts with those in nerve, skeletal, and smooth muscle.
- Membrane potential depends on ion conductance and concentration gradients.
Ion Dynamics in Cardiac Cells
- High K+ conductance at rest gives the resting membrane potential.
- Na+-K+ ATPase maintains concentration gradients of Na+ and K+ across membranes.
- Depolarization occurs with inward current (positive charge in), whereas repolarization follows an outward current (positive charge out).
Action Potential Characteristics
- Cardiac cells display an unstable resting membrane potential, differing from contractile cells.
- Slow depolarization in SA nodal cells establishes a pacemaker potential leading to action potential initiation.
Phases of Conducting Cell Action Potentials
- Phase 0 involves depolarization, primarily due to increased calcium conductance through L-type Ca2+ channels.
Autonomic Nervous System Effects
- Chronotropic effects:
- Positive: Increases heart rate via sympathetic stimulation.
- Negative: Decreases heart rate via parasympathetic stimulation.
- Dromotropic effects:
- Positive: Increases conduction velocity via sympathetic stimulation.
- Negative: Decreases conduction velocity through parasympathetic actions.
SA Node Activity Modulation
- Sympathetic stimulation enhances phase 4 depolarization frequency, increasing heart rate.
- Parasympathetic stimulation slows phase 4 depolarization, reducing heart rate.
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Description
Explore the fascinating world of cardiac muscle in this quiz. Learn about how cardiac muscle cells communicate and control the heart's rhythmical beating. Test your knowledge on the structure and functionality of the heart.
