Podcast
Questions and Answers
Which of the following best describes the primary function of cardiac myocytes?
Which of the following best describes the primary function of cardiac myocytes?
- Pumping blood (correct)
- Initiating depolarization
- Regulating heart rate
- Generating action potentials
The heart requires constant neural input from the brain to initiate each depolarization and contraction.
The heart requires constant neural input from the brain to initiate each depolarization and contraction.
False (B)
What percentage of cardiac cells are typically pacemaker cells?
What percentage of cardiac cells are typically pacemaker cells?
1
The ability of pacemaker cells to generate action potentials intrinsically is referred to as ______.
The ability of pacemaker cells to generate action potentials intrinsically is referred to as ______.
Match the following components of the conduction pathway with their correct order:
Match the following components of the conduction pathway with their correct order:
What is the correct sequence of excitation through the heart?
What is the correct sequence of excitation through the heart?
The sympathetic nervous system decreases heart rate via the vagus nerve and secretion of Acetylcholine.
The sympathetic nervous system decreases heart rate via the vagus nerve and secretion of Acetylcholine.
Which neurotransmitter is released by the parasympathetic nervous system to slow down heart rate?
Which neurotransmitter is released by the parasympathetic nervous system to slow down heart rate?
Norepinephrine, which increases heart rate, is released by the ______ nervous system.
Norepinephrine, which increases heart rate, is released by the ______ nervous system.
Match the following nervous system components with their effect on the heart rate.
Match the following nervous system components with their effect on the heart rate.
What ion movement is primarily responsible for the pacemaker potential (the slow depolarization) in cardiac pacemaker cells?
What ion movement is primarily responsible for the pacemaker potential (the slow depolarization) in cardiac pacemaker cells?
In pacemaker cells, the membrane potential remains flat (stable) and does not spontaneously depolarize because of stable ion channel activity.
In pacemaker cells, the membrane potential remains flat (stable) and does not spontaneously depolarize because of stable ion channel activity.
What causes the depolarization phase of the action potential in cardiac pacemaker cells?
What causes the depolarization phase of the action potential in cardiac pacemaker cells?
Repolarization in cardiac pacemaker cells is primarily due to the inactivation of $Ca^{2+}$ channels and the opening of ______ channels.
Repolarization in cardiac pacemaker cells is primarily due to the inactivation of $Ca^{2+}$ channels and the opening of ______ channels.
Match the phase of pacemaker cell's action potential with the corresponding ion movement:
Match the phase of pacemaker cell's action potential with the corresponding ion movement:
What is the primary cause of the plateau phase in the action potential of ventricular cardiac myocytes?
What is the primary cause of the plateau phase in the action potential of ventricular cardiac myocytes?
The plateau phase is absent in ventricular myocytes because their action potentials are shorter and faster compared to atrial myocytes.
The plateau phase is absent in ventricular myocytes because their action potentials are shorter and faster compared to atrial myocytes.
Which ion is crucial for muscle contraction during the plateau phase of ventricular cardiac myocytes action potential?
Which ion is crucial for muscle contraction during the plateau phase of ventricular cardiac myocytes action potential?
In ventricular myocytes, repolarization occurs due to the closure of $Ca^{2+}$ channels and efflux of ______.
In ventricular myocytes, repolarization occurs due to the closure of $Ca^{2+}$ channels and efflux of ______.
Match the phase of ventricular myocyte action potential with the corresponding ion movement:
Match the phase of ventricular myocyte action potential with the corresponding ion movement:
Why do action potentials in the ventricles look different from those in the atria?
Why do action potentials in the ventricles look different from those in the atria?
The duration of the refractory period in cardiac muscle is relatively short, ensuring rapid heart rates can be achieved under stress.
The duration of the refractory period in cardiac muscle is relatively short, ensuring rapid heart rates can be achieved under stress.
What is the primary cause of the absolute refractory period in cardiac muscle cells?
What is the primary cause of the absolute refractory period in cardiac muscle cells?
The refractory period in the heart is important because it prevents ______, ensuring controlled and rhythmic contractions.
The refractory period in the heart is important because it prevents ______, ensuring controlled and rhythmic contractions.
Match the term with its corresponding function/description:
Match the term with its corresponding function/description:
Flashcards
Cardiac Muscle
Cardiac Muscle
Muscle that contracts and pumps blood throughout the body.
Pacemaker Cells
Pacemaker Cells
Intrinsically generate action potentials; 1% of cardiac muscle cells.
Cardiac Myocytes
Cardiac Myocytes
Responsible for the heart's pumping ability; 99% of cardiac muscle cells.
Pacemaker Cells
Pacemaker Cells
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Conduction Pathway
Conduction Pathway
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Excitation Sequence
Excitation Sequence
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Sympathetic Nervous System effect on heart?
Sympathetic Nervous System effect on heart?
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Parasympathetic Nervous System effect on heart?
Parasympathetic Nervous System effect on heart?
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Pacemaker Potential
Pacemaker Potential
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Depolarization (pacemaker cells)
Depolarization (pacemaker cells)
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Repolarization (pacemaker cells)
Repolarization (pacemaker cells)
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Depolarization (cardiac myocytes)
Depolarization (cardiac myocytes)
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Ca2+ influx is necessary for what?
Ca2+ influx is necessary for what?
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Refractory Period
Refractory Period
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Why is the Refractory Period important?
Why is the Refractory Period important?
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Why do action potentials in ventricles look different from those in the atria?
Why do action potentials in ventricles look different from those in the atria?
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Study Notes
- The heart is a muscle that contracts and pumps blood.
Cardiac Muscle Cells
- Cardiac muscle cells are responsible for electrical impulses.
- Cardiac muscle cells are responsible for electrical impulses.
- Pacemaker cells intrinsically generate action potentials, compromising 1% of cardiac muscle cells.
- Cardiac myocytes are contractile cells responsible for the heart's pumping ability, making up 99% of cardiac muscle cells.
- Unlike skeletal muscle, the heart doesn't require neural input from the brain to initiate depolarization and contraction.
- Neural input to the heart helps alter its basic rhythm by making it faster or slower.
- Hearts can be removed from the body and still beat because of pacemaker cells.
Electrical Conduction in the Heart
- Electrical impulses are a result of ion flow changes across the cell membrane.
- Pacemaker cells are 1% of the cells, are autorhythmic, and continually generate action potentials.
- Myocytes make up the myocardium.
Conduction Pathway
- Pacemaker cells are cardiac cells that generate and conduct action potentials.
- Pacemaker cells are also called autorhythmic cells.
- Pacemaker cells also help make up the conduction pathway.
- The conduction pathway includes the SA node, AV node, AV bundle (Bundle of His), Bundle branches, and Purkinje fibers.
Excitation Sequence
- Impulses generated via pacemaker cells spread to and through surrounding cardiac myocytes in order to initiate muscle contraction.
- The sequence is SA node to AV node to AV bundle to Bundle branches to Purkinje fibers
- Atrial contraction occurs, moving to ventricular contraction, finally out of the heart.
Modifying the Basic Rhythm
- The heart rate has fluctuations
- The sympathetic nervous system (NS) acts as an "accelerator".
- Cardiac nerves innervate SA and AV nodes.
- Norepinephrine is then released.
- The parasympathetic nervous system acts as "brakes".
- The vagus nerve acts at the SA and AV nodes.
- Acetylcholine is released to slow down the heart rate.
Pacemaker Cells and Action Potentials
- Pacemaker cells generate action potentials that spread throughout the heart.
- Pacemaker cells have an unstable resting membrane potential called pacemaker potentials.
- Pacemaker potential exhibits slow depolarization due to the opening of Na+ channels and Na+ influx; the membrane potential never flat-lines.
- Depolarization occurs when the pacemaker potential reaches the threshold, causing the opening of Ca2+ channels and Ca2+ influx.
- Repolarization is when Ca2+ channels inactivate, K+ channels open, and K+ efflux brings the membrane potential back to its most negative voltage.
Depolarization
- Impulses generated by pacemaker cells lead to depolarization of the surrounding contractile cardiac myocytes.
- Depolarization involves the opening of Na+ channels and rapid Na+ influx.
- Plateau is maintained during depolarization.
- Some K+ channels open, and K+ efflux causes a slight dip.
- Ca2+ channels open, and Ca2+ influx is necessary for muscle contraction.
- Repolarization occurs, causing Ca2+ channels to inactivate and more K+ channels to open.
- K+ efflux brings the membrane potential back down.
Potentials in Conduction Pathway
- More muscle around the ventricle requires more Ca2+, which is responsible for why the plateau phase looks different in atrial versus ventricular muscle.
Refractory Period
- Refractory period is a time following an action potential when a new action potential cannot be initiated.
- It is caused by the inactivation of sodium channels.
- It's important because it ensures that the heart beats in a controlled, rhythmic manner, preventing over-stimulation, and allowing time for the heart to properly fill blood.
Action Potentials in Ventricles
- Action potentials in the ventricles look different than those in the atria because there is more muscle around the ventricles which require more Ca2+.
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