Cardiac Action Potentials and Myogenic Activity
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Questions and Answers

What role do L-type channels play in cardiac muscle contraction?

  • They allow potassium to flow out during repolarization.
  • They permit Ca2+ to flow in from the T-tubules across the cell membrane. (correct)
  • They activate ryanodine receptors for muscle relaxation.
  • They shuttle Ca2+ from the sarcoplasmic reticulum to the myofibrils.
  • Why is the effective refractory period longer in cardiomyocytes than in skeletal muscle?

  • Skeletal muscle has less reliance on sodium channels.
  • Cardiomyocytes have more potassium currents.
  • Cardiomyocytes cannot be re-stimulated due to prolonged Ca2+ influx. (correct)
  • The action potentials last longer in cardiomyocytes.
  • What initiates the release of more Ca2+ from the sarcoplasmic reticulum during cardiac contraction?

  • Influx of calcium via L-type channels. (correct)
  • Activation of sodium channels.
  • Release of potassium from the sarcoplasmic reticulum.
  • Contraction of myofibrils.
  • What are ryanodine receptors responsible for in cardiomyocytes?

    <p>Releasing calcium stored in the sarcoplasmic reticulum. (D)</p> Signup and view all the answers

    Which feature contributes to the complexity of potassium permeability in cardiac muscle?

    <p>The presence of multiple distinct K+ currents. (C)</p> Signup and view all the answers

    What is the primary function of the cardiac skeleton?

    <p>Providing structural support (B)</p> Signup and view all the answers

    Which of the following is essential for maintaining the flow of action potentials between cardiac muscle cells?

    <p>Gap junctions (C)</p> Signup and view all the answers

    How does the conduction system affect the timing of electrical waves in the heart?

    <p>It causes electrical waves to pause between atria and ventricles (D)</p> Signup and view all the answers

    What type of cells are predominantly responsible for generating action potentials in the heart?

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

    What is the role of T-tubules in cardiac muscle cells?

    <p>Conducting action potentials deep into the muscle cells (D)</p> Signup and view all the answers

    Which of the following components is essential for cardiac muscle contraction and energy supply?

    <p>Sarcoplasmic reticulum (C)</p> Signup and view all the answers

    What type of tissue surrounds the conduction system of the heart and provides insulation?

    <p>Collagenous tissue (B)</p> Signup and view all the answers

    In cardiomyocytes, what is the primary function of the mitochondria?

    <p>To supply energy (C)</p> Signup and view all the answers

    Which cells in the heart are primarily responsible for generating action potentials spontaneously?

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

    What type of ion influx primarily occurs through funny channels in pacemaker cells?

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

    What is the main function of T-type calcium channels in pacemaker cells?

    <p>Allow Ca2+ to enter transiently (A)</p> Signup and view all the answers

    What role do L-type calcium channels play in cardiac cells?

    <p>Permit long-term Ca2+ entry (C)</p> Signup and view all the answers

    How do pacemaker cells differ from typical neurons in terms of action potential generation?

    <p>They generate APs without neural stimulation. (B)</p> Signup and view all the answers

    What is a common feature of both funny and T-type calcium channels?

    <p>They are voltage-gated. (C)</p> Signup and view all the answers

    Which ion is primarily involved in the depolarization phase of action potentials in cardiac pacemaker cells?

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

    How does the presence of cAMP affect ion channels in pacemaker cells?

    <p>It activates both funny and L-type calcium channels. (B)</p> Signup and view all the answers

    Flashcards

    Myogenic Heart

    A heart that can beat independently of nerve stimulation.

    Sinoatrial Node (SAN)

    The pacemaker of the heart, initiating the electrical impulse for each heartbeat.

    Spontaneous Generation of APs

    The ability of pacemaker cells to produce action potentials without external triggering.

    Funny Channels

    Special ion channels in pacemaker cells that open at negative membrane potentials, allowing Na+ influx.

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    T-Type Calcium Channels

    Voltage-gated calcium channels that open briefly in pacemaker cells, allowing Ca2+ influx.

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    L-Type Calcium Channels

    Voltage-gated calcium channels that open for a longer duration in both pacemaker cells and cardiomyocytes.

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    cAMP Activation of Channels

    Cyclic adenosine monophosphate (cAMP), a second messenger, can activate funny and T-type calcium channels.

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    G-Protein Mediated Channels

    Many ion channels are indirectly regulated through G-proteins, which are activated by neurotransmitters and drugs.

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    T-tubules

    Extensions of the sarcolemma (cell membrane) that penetrate deep into the cardiac muscle cell, allowing for rapid and efficient calcium ion delivery.

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    Sarcoplasmic Reticulum (SR)

    A network of intracellular membrane-bound sacs that store and release calcium ions (Ca++) during muscle contraction.

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    Ryanodine Receptors

    Calcium-sensitive channels located on the sarcoplasmic reticulum that are activated by calcium ions, triggering the release of more calcium from the SR.

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    Effective Refractory Period

    The period during which a cardiac muscle cell cannot be re-stimulated, even with a strong stimulus, ensuring proper heart rhythm and preventing tetanic contractions.

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    Pacemaker Cells

    Specialized cardiac muscle cells that initiate and control the heart's rhythm by spontaneously generating electrical impulses.

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    Cardiac Skeleton

    A framework of fibrous tissue that supports the heart's structure, guides electrical conduction, and isolates electrical waves.

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    Gap Junctions

    Specialized cell junctions that allow electrical signals to pass directly between neighboring cardiac muscle cells, ensuring synchronized contraction.

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    What is the function of Gap junctions?

    Gap junctions allow electrical signals to pass directly between neighboring cardiac muscle cells, ensuring synchronized contraction of the heart.

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    Why is the Cardiac Skeleton important?

    The Cardiac Skeleton provides structural support, guides electrical conduction, and isolates electrical waves between the atria and ventricles.

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    What is the role of T-tubules in cardiac muscle cells?

    T-tubules are extensions of the sarcolemma (cell membrane) that penetrate deep into cardiac muscle cells, allowing electrical impulses to reach the interior of the cell quickly and efficiently.

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    What is the Sarcoplasmic Reticulum's role in heart muscle contraction?

    The Sarcoplasmic Reticulum is a network of membrane-bound sacs within muscle cells that stores and releases calcium ions (Ca++) during muscle contraction.

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    Study Notes

    Learning Goals

    • Students are expected to understand action potentials (APs), myogenic APs, conduction of AP waves, and contraction of cardiac muscle cells.

    Hearts are Myogenic

    • Hearts can beat independently of neural stimulation.
    • This is demonstrated through examples of isolated heart cells in a Petri dish that continue to beat.
    • Additional examples of myogenic activity include videos linked in the document.

    Pacemaker Cells

    • The sinoatrial node (SAN) is the starting point.
    • Cardiac tissue in the SAN spontaneously generates action potentials.

    Action Potential (AP) in a Pacemaker Cell

    • Graph describing membrane potential and time.

    Funny Channels

    • There are specific types of channels in pacemaker cells (and not other cardiac cells).
    • These are voltage-gated channels, but they also respond to cyclic AMP.
    • The influx of sodium and calcium ions is the result of these channels.
    • Specific types of sodium and calcium channels are unique to, and only found in, pacemaker cells.

    Take Home Messages

    • Funny channels are involved in the initial sodium influx in pacemaker cells.
    • T-type calcium channels allow for short bursts of calcium.
    • L-type calcium channels allow for prolonged calcium influx.
    • Pacemaker cells utilize different types of channels for their unique function compared to other cardiac cells.

    General Point to Biologists

    • G-proteins often modulate the action of other channels.

    Cardiac Skeleton

    • Provides structural support within the heart.
    • Separates the atria and ventricles.
    • Insulates and directs the passage of electrical signals across the heart.

    Conduction System

    • Special fibers, embedded in collagenous tissue.
    • These fibers are known as pacemaker cells.
    • This conduction system is essential to coordinate the contraction of the heart.

    Components of Cardiac Muscle Cells

    • Membrane (sarcolemma): Outer covering of the cell.
    • Myofibrils: Contractile units within the cell.
    • T-tubules: Extensions of the sarcolemma that reach deep into the cell.
    • Sarcomeres: Functional units of the myofibrils.
    • Mitochondria: Generate energy for the contraction.
    • Sarcoplasmic Reticulum: Stores and releases calcium ions.

    Cardiac Muscle Conductivity

    • Cardiac muscle cells are specialized to conduct impulses.

    Gap Junctions

    • Gap junctions ensure that action potentials flow between cells.
    • These junctions are crucial for proper heart function.

    Cardiac Muscle Contraction

    • Calcium influx from different sources is essential for contraction.
    • Activation of ryanodine receptors amplifies calcium release.

    Cardiac Action Potential

    • The cardiac action potential duration is prolonged, allowing for sufficient relaxation time.
    • This differs substantially from skeletal muscle cells

    Questions to Consider

    • Differences in rising slopes of action potentials in various cells are notable.

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    Description

    This quiz explores the fundamentals of action potentials in cardiac muscle cells, specifically focusing on myogenic activity and the role of pacemaker cells. Students will learn about the sinoatrial node and its ability to generate action potentials independently of neural input. Additionally, the quiz covers the unique channels involved in pacemaker activity.

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