13 Questions
What is the main factor that prevents cardiac muscle from remaining in a state of sustained (tetanic) contraction?
Refractory period after an action potential
Which ion channels contribute to the initial depolarization phase (phase 0) of the cardiac action potential?
Fast sodium channels
What is the main difference in the action potential shapes of nodal, atrial muscle, ventricular muscle, and Purkinje fiber cardiac cells?
Differences in the duration and shape of phase 4
What is the primary reason for the long duration of the cardiac action potential?
The plateau phase
Which component of the cardiac conduction system is responsible for maintaining the delay between atrial and ventricular excitation?
AV node
What is the primary driver of pacemaker automaticity and rhythmicity in the heart?
Ionic mechanism
Which type of cardiac myocytes exhibit fast response action potentials?
Conducting/contracting myocytes
What is the main function of the long refractory period in cardiac action potential?
Preventing tetany
Which cells are responsible for initiating the normal sequence of cardiac activation?
SA node cells
What is the function of the AV node in the heart's electrical pathway?
Conducting electrical signals between atria and ventricles
Which cells in the heart have the highest intrinsic rate and serve as the primary pacemaker cells?
SA node cells
Which specialized cells are involved in the conduction system of the heart?
SA node, AV node, bundle of His, Purkinje fibers
How do the electrical events in the heart initiate cardiac contractions?
Through rhythmical electrical activity coordinating mechanical activity
Study Notes
Cardiac Conduction System and Action Potential Summary
- Cardiac action potential duration is long due to the plateau phase, which results in a long refractory period.
- The long refractory period provides an advantage by preventing tetany and allowing for efficient coordination of mechanical activity in the heart.
- The normal sequence of cardiac activation begins in the SA node and involves specialized cells such as AV node cells, Purkinje cells, and conducting cardiac myocytes.
- The AV node is the only normal electrical pathway between the atria and ventricles, and its slow conduction is functionally significant for maintaining the delay between atrial and ventricular excitation.
- Pacemaker automaticity and rhythmicity are driven by the ionic mechanism, with SA node cells being primary pacemaker cells and having the highest intrinsic rate.
- The sympathetic and parasympathetic nervous systems influence heart rate and cardiac excitation through specific ionic mechanisms in working myocardium and pacemaker cells.
- Voltage-gated sodium channel blockers, calcium channel blockers, potassium channel blockers, and changes in serum potassium levels all affect cardiac electrical activity.
- The conduction system of the heart involves specialized cells such as the SA node, AV node, bundle of His, and Purkinje fibers, each with specific conduction and pacemaker activity rates.
- The electrical events in the heart initiate cardiac contractions through rhythmical electrical activity coordinating mechanical activity.
- Cardiac myocytes exhibit two types of action potentials: fast response in conducting/contracting myocytes and slow response in pacemaker cells.
- The action potential in ventricular cardiac myocytes involves phases of rapid depolarization, early partial repolarization, plateau phase, final repolarization, and resting potential.
- The long refractory period in ventricular myocytes is protective and limits the frequency of action potentials and contractions, and it ends at the end of phase 3.
Cardiac Conduction System and Action Potential Summary
- Cardiac action potential duration is long due to the plateau phase, which results in a long refractory period.
- The long refractory period provides an advantage by preventing tetany and allowing for efficient coordination of mechanical activity in the heart.
- The normal sequence of cardiac activation begins in the SA node and involves specialized cells such as AV node cells, Purkinje cells, and conducting cardiac myocytes.
- The AV node is the only normal electrical pathway between the atria and ventricles, and its slow conduction is functionally significant for maintaining the delay between atrial and ventricular excitation.
- Pacemaker automaticity and rhythmicity are driven by the ionic mechanism, with SA node cells being primary pacemaker cells and having the highest intrinsic rate.
- The sympathetic and parasympathetic nervous systems influence heart rate and cardiac excitation through specific ionic mechanisms in working myocardium and pacemaker cells.
- Voltage-gated sodium channel blockers, calcium channel blockers, potassium channel blockers, and changes in serum potassium levels all affect cardiac electrical activity.
- The conduction system of the heart involves specialized cells such as the SA node, AV node, bundle of His, and Purkinje fibers, each with specific conduction and pacemaker activity rates.
- The electrical events in the heart initiate cardiac contractions through rhythmical electrical activity coordinating mechanical activity.
- Cardiac myocytes exhibit two types of action potentials: fast response in conducting/contracting myocytes and slow response in pacemaker cells.
- The action potential in ventricular cardiac myocytes involves phases of rapid depolarization, early partial repolarization, plateau phase, final repolarization, and resting potential.
- The long refractory period in ventricular myocytes is protective and limits the frequency of action potentials and contractions, and it ends at the end of phase 3.
Test your knowledge of the cardiac conduction system and action potential with this quiz. Explore topics such as the sequence of cardiac activation, refractory periods, pacemaker cells, influence of the autonomic nervous system, and the effects of various blockers on cardiac electrical activity.
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