Cardiac Physiology Quiz
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Questions and Answers

What causes the contraction of heart cells?

  • The binding of ATP to myosin
  • The release of neurotransmitters from the autonomic nervous system
  • The release of calcium ions from the sarcoplasmic reticulum
  • The influx of sodium ions into the cell (correct)

    • What is the effect of heart cell contraction?

  • The filtration of waste products in the kidneys
  • The exchange of gases in the lungs
  • The pumping of blood throughout the body (correct)
  • The regulation of blood pressure

    • Which of the following techniques can be used to study the electrical activity of the heart?

  • Computed Tomography (CT) scan
  • Electrocardiography (ECG) (correct)
  • Echocardiography
  • Magnetic Resonance Imaging (MRI)

    • Which of the following ions plays a key role in the depolarization of a heart cell?

    <p>Sodium (Na+) (D)</p> Signup and view all the answers

    What is the primary function of the sinoatrial (SA) node?

    <p>To control the rate and rhythm of heart contractions (D)</p> Signup and view all the answers

    In cardiac pacemaker cells, what ion influx is primarily responsible for the slow depolarization of the pacemaker potential?

    <p>Sodium (Na+) (A)</p> Signup and view all the answers

    What is the main role of calcium ions (Ca2+) in non-pacemaker cardiac muscle cells during an action potential?

    <p>Ca2+ influx prolongs the action potential and creates a plateau phase. (C)</p> Signup and view all the answers

    What is the primary function of the intercalated disks with gap junctions in cardiac muscle?

    <p>They allow rapid and efficient conduction of electrical signals between cardiac muscle cells. (B)</p> Signup and view all the answers

    Why is the conduction of electrical signals through the AV node slower than in other parts of the heart's conduction system?

    <p>The AV node has a smaller number of gap junctions, reducing the efficiency of electrical signal transmission. (A)</p> Signup and view all the answers

    What is meant by the statement "All cells of the intrinsic conduction system have the ability to generate spontaneous action potentials - i.e. they are autorhythmic"?

    <p>These cells can generate action potentials without any external stimulation, acting as pacemakers. (B)</p> Signup and view all the answers

    Which of the following is NOT a component of the intrinsic conduction system of the heart?

    <p>Intercalated disks (B)</p> Signup and view all the answers

    What is the role of the internodal pathways in the heart's electrical conduction system?

    <p>They conduct electrical signals from the SA node to the AV node. (D)</p> Signup and view all the answers

    What is the primary function of the Purkinje fibers in the heart?

    <p>They conduct the electrical signal quickly through the ventricles. (A)</p> Signup and view all the answers

    Which of the following statements regarding sympathetic stimulation of the SA node is TRUE?

    <p>Sympathetic stimulation leads to an increase in the activity of the funny current (HCN) channels. (B)</p> Signup and view all the answers

    Which of the following is NOT a direct effect of norepinephrine on the SA node cells?

    <p>Increase in the permeability of potassium channels (A)</p> Signup and view all the answers

    What is the role of cAMP in the sympathetic stimulation of the SA node?

    <p>cAMP activates protein kinase A, which then phosphorylates and activates L-type calcium channels and HCN channels. (D)</p> Signup and view all the answers

    How does the parasympathetic nervous system influence heart rate?

    <p>It increases the permeability of potassium channels, leading to a slower rate of depolarization. (A)</p> Signup and view all the answers

    Which of the following is TRUE regarding autorhythmic cells?

    <p>They produce their own rhythmic depolarizations, not requiring external stimulation. (B)</p> Signup and view all the answers

    What is the primary mechanism by which the sympathetic nervous system increases heart rate?

    <p>It increases the activity of the funny current (HCN) channels, leading to faster depolarization of the SA node. (D)</p> Signup and view all the answers

    What is the primary mechanism by which the parasympathetic nervous system decreases heart rate?

    <p>It increases the permeability of potassium channels in the SA node, leading to a slower rate of depolarization. (C)</p> Signup and view all the answers

    What is the function of the beta-adrenergic receptors on the SA node cells?

    <p>They bind to norepinephrine, initiating the sympathetic response. (B)</p> Signup and view all the answers

    Which of the following is NOT a factor that influences the heart rate?

    <p>Blood volume (C)</p> Signup and view all the answers

    Which part of the heart is directly innervated by parasympathetic fibers to influence the heart's electrical activity?

    <p>Sinoatrial node (B), Atrioventricular node (C)</p> Signup and view all the answers

    What does the P wave on an ECG represent?

    <p>Depolarization of the atria (D)</p> Signup and view all the answers

    Which of the following is a major benefit of using an electrocardiogram (ECG)?

    <p>It is a non-invasive, simple, and affordable procedure. (B)</p> Signup and view all the answers

    What does the QRS complex on an ECG represent?

    <p>Depolarization of the ventricles (B)</p> Signup and view all the answers

    What does a longer P-R interval on an ECG indicate?

    <p>Delayed conduction through the AV node (C)</p> Signup and view all the answers

    What is the typical normal range for heart rate?

    <p>60-100 beats per minute (D)</p> Signup and view all the answers

    What is the primary difference between the electrocardiogram (ECG) and the ventricular action potential?

    <p>The ECG records the summed electrical activity of all cells from the surface of the body, while the ventricular action potential records from a single cell. (B)</p> Signup and view all the answers

    What is the approximate resting heart rate set by the SA node?

    <p>70 bpm (D)</p> Signup and view all the answers

    Which of the following is NOT a function of the AV node?

    <p>Sets the pace of the heartbeat (A)</p> Signup and view all the answers

    Why are atrial and ventricular myocyte syncytia separated by an inert fibrous tissue barrier?

    <p>To allow for independent contraction of the atria and ventricles (D)</p> Signup and view all the answers

    What is the neurotransmitter released by the vagus nerve that lowers heart rate by activating muscarinic receptors (M2R) in SA node cells?

    <p>Acetylcholine (Ach) (C)</p> Signup and view all the answers

    Which of the following is an antagonist of muscarinic receptors (M2R) and can lead to an increase in heart rate?

    <p>Atropine (A)</p> Signup and view all the answers

    What is the role of the Purkinje fibers in the heart's electrical conduction system?

    <p>To rapidly conduct the electrical signal throughout the ventricles (B)</p> Signup and view all the answers

    Why is the AV node considered a control point for the heart's electrical conduction?

    <p>It delays the transmission of the electrical signal, ensuring proper ventricular filling (C)</p> Signup and view all the answers

    What causes the unstable resting potential in cardiac autorhythmic cells?

    <p>Slow influx of sodium ions through funny current channels (If) (B)</p> Signup and view all the answers

    Which of the following is true of cardiac myocyte action potentials?

    <p>They are triggered by depolarization from neighboring cells. (A)</p> Signup and view all the answers

    What is the role of funny current channels (If) in cardiac autorhythmic cells?

    <p>To cause the slow depolarization of the pacemaker potential (A)</p> Signup and view all the answers

    What is the main function of the pacemaker (autorhythmic) cells?

    <p>To initiate and regulate the heart's rhythm (D)</p> Signup and view all the answers

    What type of ion channels are responsible for the plateau phase of the cardiac action potential?

    <p>Calcium channels (D)</p> Signup and view all the answers

    What would happen to the heart rate if the funny current (If) was blocked?

    <p>Heart rate would decrease (B)</p> Signup and view all the answers

    Which of the following cell types would be found in the sinoatrial node?

    <p>Pacemaker cells (C)</p> Signup and view all the answers

    What is the main difference between cardiac autorhythmic cell action potentials and cardiac myocyte action potentials?

    <p>Autorhythmic cells generate their own action potentials, while myocytes don't. (D)</p> Signup and view all the answers

    Flashcards

    Cardiac excitability

    The ability of heart cells to respond to stimuli and generate action potentials.

    Heart contraction

    The process by which heart muscle cells shorten and generate force to pump blood.

    Causes of heart contraction

    Heart cells contract primarily due to the influx of calcium ions during action potentials.

    Effects of electrical signals

    Electrical signals lead to coordinated heart contractions essential for effective blood circulation.

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    Using contractions to study the heart

    Researchers analyze heart contractions and electrical activity to diagnose and understand heart conditions.

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    Type 1 Action Potential

    Fast response action potentials in non-pacemaker cells (myocytes) causing rapid depolarization.

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    Type 2 Action Potential

    Pacemaker action potentials arising from autorhythmic cells with unstable resting potential.

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    Autorhythmic Cells

    Non-contractile cells responsible for creating heart rhythm, found in SA and AV nodes.

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    Funny Current Channels

    If channels that allow K+ and Na+ to contribute to the unstable resting potential in pacemaker cells.

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    Pacemaker Potential

    The gradual depolarization in pacemaker cells that leads to action potential when threshold is reached.

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    Threshold in Cardiac AP

    The membrane potential level that, when reached, triggers an action potential in pacemaker cells.

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    Ion Movements during Action Potential

    The flow of Ca2+, Na+, and K+ ions during depolarization and repolarization in cardiac cells.

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    Non-pacemaker Cells

    Contractile cardiac myocytes that rely on signals from pacemaker cells to initiate depolarization.

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    Na+ role in cardiac cells

    Na+ channels open, causing rapid depolarization in non-pacemaker cardiac muscle cells.

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    Ca2+ role in cardiac muscle

    Ca2+ influx prolongs action potential duration and creates a plateau phase in non-pacemaker cells.

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    Ca2+ in pacemaker cells

    Ca2+ ions initiate depolarization during the action potential in pacemaker cells.

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    SA node

    Sinoatrial node; primary pacemaker of the heart that initiates electrical signals.

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    Electrical conduction in the heart

    Autorhythmic signals spread through the heart via intercalated disks and gap junctions.

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    AV node function

    Atrioventricular node; slows conduction of electrical activity from atria to ventricles.

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    Intrinsic conduction system

    Network of cells capable of generating spontaneous action potentials, ensuring heart rhythm.

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    Sympathetic nerves

    Nerves that increase heart rate by releasing norepinephrine on the SA node.

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    Norepinephrine (NE)

    A neurotransmitter that binds to beta-adrenergic receptors, increasing heart rate.

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    Beta-adrenergic receptors (bARs)

    Receptors on SA node cells that bind norepinephrine to increase heart activity.

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    cAMP (cyclic AMP)

    A molecule that increases in response to sympathetic stimulation, enhancing heart rate.

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    PKA (protein kinase A)

    An enzyme activated by cAMP that increases calcium channel activity in heart cells.

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    L-type Ca2+ channels

    Channels that allow calcium ions to enter heart cells, crucial for contraction facilitation.

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    Vagus nerves

    Parasympathetic nerves that decrease heart rate by affecting the SA node.

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    Purkinje Fibers

    Fibers that distribute the depolarization wave throughout the ventricles, allowing coordinated contractions.

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    Sympathetic Control

    Part of the autonomic nervous system that increases heart rate during stress or activity.

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    Parasympathetic Control

    Part of the autonomic nervous system that lowers heart rate, primarily via the vagus nerve.

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    Vagal Tone

    The baseline level of parasympathetic activity that maintains resting heart rate between 60 and 80 bpm.

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    Acetylcholine (Ach)

    A neurotransmitter released by the vagus nerve that slows down heart rate by acting on the SA node.

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    Heart Rate Regulation

    Controlled by balancing sympathetic and parasympathetic activities affecting SA node firing.

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    Parasympathetic fibers

    Nerves that control the heart rate by innervating the SA and AV nodes without affecting contraction force.

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    Sympathetic fibers

    Nerves that increase heart rate and contraction strength by innervating SA node, AV node, atria, and ventricles.

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    Electrocardiogram (ECG)

    A noninvasive test that records the electrical activity of the heart through three main waves.

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    P wave

    The wave in an ECG that represents atrial depolarization before contraction.

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    QRS complex

    The section of the ECG that reflects ventricular depolarization and subsequent contraction.

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    T wave

    The wave on the ECG that represents ventricular repolarization, when the heart muscle resets.

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    ECG analysis questions

    Key inquiries to assess an electrocardiogram: rate, rhythm, wave presence, and QRS to P wave ratio.

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    Heart rate normal range

    A typical heart rate of 60 to 100 beats per minute, indicating a healthy rhythm.

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    Study Notes

    Cardiac Excitability: Heart Rate and ECG

    • Underlying Reason for Heart Contraction: The lecture discusses the mechanisms behind heart cell contraction, focusing on the cause, effect, and how this information is used to study the heart.

    Two Types of Cardiac Action Potentials

    • Type 1: Non-pacemaker Cells (Myocytes):

      • These cells exhibit "fast response" action potentials, characterized by rapid depolarization in response to an action potential (AP).
      • They're considered "soldiers," needing instructions to fire.
      • These cells make up most of the atrial and ventricular muscle walls.
      • Action potential characteristics are shown graphically, highlighting differences compared to nerve cells.

    • Type 2: Pacemaker (Autorhythmic) Cells:

      • Possess unstable resting potentials, which causes spontaneous firing.
      • These "generals" provide firing instructions to the muscular "soldiers".
      • Found in the sinoatrial (SA) and atrioventricular (AV) nodes.
      • The graph showcases the various ion movements that generate action potentials in these cells.

    Action Potentials in Cardiac Autorhythmic Cells

    • Funny Current Channels (If):
      • Funny current channels (If) contribute to the unstable resting potential.
      • These channels allow both potassium (K⁺) and sodium (Na⁺) permeability.
      • Depolarization happens as pacemaker potential progressively becomes less negative until it reaches a threshold, initiating the action potential.
      • Ion movements during action and pacemaker potentials are visually presented.

    Role of Na⁺ and Ca²⁺

    • Cardiac Muscle (Non-pacemaker):

      • Sodium (Na⁺) channels are responsible for rapid depolarization.
      • Calcium (Ca²⁺) influx prolongs the action potential and produces the plateau phase.
      • Calcium is involved in the initial depolarization phase.

    • Cardiac Pacemaker Cells:

      • A slow depolarizing pacemaker potential (dependent on funny current) facilitates autorhythmic function.

    Electrical Conduction to Myocardial Cells

    • Autorhythmic Signal Propagation:
      • Depolarizations originating from autorhythmic cells rapidly spread to adjacent contractile cells via gap junctions.

    Intrinsic Conduction System

    • Autorhythmic Cells: All cells in the intrinsic conduction system are autorhythmic, generating spontaneous action potentials.
    • Locations (Wiring): The system includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, right and left bundle branches, and Purkinje fibers, visualized in anatomical diagrams.

    Nodes (Control Points)

    • SA Node: Sets the heart rate at approximately 70 bpm.
    • AV Node: Routes electrical signals, delays transmission of action potentials. Additional nodes (AV node, Purkinje fibers) can act as pacemakers under specific conditions. Specified ranges of beats per minute (bpm) are also noted.

    Conduction Fibres

    • Conduction Fibres: The specialized conducting fibres are sheathed, except in atrial and ventricular myocyte contact regions.
    • Fibrous Barrier: Atrial and ventricular myocyte syncytia are separated by inert fibrous tissue, lacking gap junctions that prevent unwanted propagation between atria and ventricles.

    Heart Rate Control (Sympathetic and Parasympathetic Nerves)

    • Both sympathetic and parasympathetic nervous systems regulate heart rate.

    • Parasympathetic (Vagus Nerve): Lowers heart rate by releasing acetylcholine (ACh) onto muscarinic receptors (M2Rs). Resting heart rate is approximated at 60–80 beats/min.

    • Sympathetic Nerves: Increase heart rate by releasing norepinephrine (NE). Catecholamines from the adrenal gland boost this response.

    • Specific ion channel activity is involved in the respective responses.

      • Parasympathetic activation triggers a decrease in cAMP levels, lowering activity of HCN and Ca2+ channels.
      • Sympathetic activation increases cAMP, upregulating Ca2+ and HCN (funny current) channel activity.

    Modulation of Heart Rate by the Autonomic Nervous System

    • Graphs illustrate changes in membrane potential in response to sympathetic and parasympathetic stimulation.

    Review Question

    • One of the presented options, regarding autorhythmic cells, is the correct answer. The answer is included in the previous notes.

    Control of Heart Rate vs Contraction Strength

    • Vagus Nerves (Parasympathetic): Regulate heart rate but not contraction strength. They only innervate SA and AV nodes.
    • Sympathetic Fibers: Effect both heart rate and contraction strength, also innervating the atria and ventricles.

    Additional Discussion Points

    • ECG (Electrocardiogram): Study of heart anatomy and electrical properties aid in better understanding health and diseases.
    • ECG Wave Relationships and Correlates with Electrical Activity: Explain the correlation between ECG tracings and electrical events within the heart's conduction cycle (e.g., P wave, QRS complex, T wave).
    • ECG Analysis Tips: Analysis and interpretation of ECG tracings involve factors such as heart rate, rhythm regularity, presence of normal waves, and comparing P-R and R-R intervals for uniformity.

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    Related Documents

    PSL301H – Lecture 2: Cardiac Excitability: Heart Rate and ECG PDF

    Description

    Test your knowledge of the mechanisms underlying heart cell contraction and the role of electrical activity in cardiac function. This quiz covers key concepts related to pacemaker cells, ion channels, and the conduction system of the heart.

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