Neuroscience AP Potassium Channels Quiz
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Questions and Answers

What is the resting membrane potential of a cardiac myocyte during the quiescent period?

  • +30 mV
  • 0 mV
  • -70 mV
  • -90 mV (correct)

    • Which ion channels primarily mediate the transient outward potassium current (Ito)?

  • Calcium channels
  • Chloride channels
  • Sodium channels
  • Potassium channels (correct)

    • What is the primary function of the Na+/Ca2+ exchanger (INCX) in cardiac myocytes?

  • To pump sodium into the cell
  • To maintain a stable resting membrane potential
  • To pump calcium into the cells in exchange for sodium (correct)
  • To conduct potassium out of the cell

    • During which phase do potassium ions leave the cell, leading to a more negative membrane potential?

    <p>Phase 4</p> Signup and view all the answers

    What characteristic of the inward rectifying potassium channel (Kir) allows it to function effectively at low voltages?

    <p>It allows potassium to pass out of the cell at low voltages</p> Signup and view all the answers

    What is the resting membrane potential of slow-response cells?

    <p>-60 mV</p> Signup and view all the answers

    What is the net effect of the ionic events mediated by Ik1 current in cardiac myocytes?

    <p>Loss of intracellular sodium and a more negative membrane potential</p> Signup and view all the answers

    Which phase of the cardiac action potential demonstrates a more significant amplitude in fast-response cells compared to slow-response cells?

    <p>Phase 0</p> Signup and view all the answers

    What is the significance of the quiescent period for the cardiac myocyte?

    <p>It prepares the cell for depolarizing signals</p> Signup and view all the answers

    What is the threshold potential for spontaneous action potential generation in cardiac pacemaker cells?

    <p>-40 mV</p> Signup and view all the answers

    What voltage range do inward rectifying potassium channels (Kir) become largely impermeable to potassium ions?

    <p>At voltages more positive than approximately -90 mV</p> Signup and view all the answers

    How does the conduction of action potentials differ between slow-response and fast-response cardiac tissue?

    <p>Action potentials propagate more slowly in slow-response cardiac tissue.</p> Signup and view all the answers

    What is the impact of Na+ and Ca2+ ions in the depolarization process of cardiac cells?

    <p>They leak into the cells, making the membrane potential more positive.</p> Signup and view all the answers

    What triggers the rapid depolarization in Phase 0 of the cardiac action potential?

    <p>Fast opening of Na+ channels</p> Signup and view all the answers

    Which phase of the cardiac action potential is characterized by the transient opening of K currents?

    <p>Phase 1</p> Signup and view all the answers

    What happens to the membrane potential during Phase 0 of the cardiac action potential?

    <p>It increases to +50 mV</p> Signup and view all the answers

    What is the primary ionic event involved in Phase 2 of the cardiac action potential?

    <p>Opening of Ca2+ channels</p> Signup and view all the answers

    Which statement accurately describes the end of Phase 1?

    <p>An overshoot potential is achieved</p> Signup and view all the answers

    What characterizes Phase 4 of the cardiac action potential?

    <p>Stable resting membrane potential</p> Signup and view all the answers

    During which phase do K+ channels open, allowing repolarization to occur?

    <p>Phase 3</p> Signup and view all the answers

    What happens during Phase 1 of the cardiac action potential?

    <p>K+ channels open and Na+ channels close</p> Signup and view all the answers

    What characterizes phase 4 of the action potential in autorhythmic cells?

    <p>It involves slow depolarization due to Na+ and Ca2+ leaks.</p> Signup and view all the answers

    In which part of the cardiac muscle are autorhythmic cells primarily found?

    <p>Sinoatrial node</p> Signup and view all the answers

    How do the durations of contraction and action potential compare in cardiac myocytes?

    <p>Contraction lasts longer than the action potential.</p> Signup and view all the answers

    What is the primary function of the sinoatrial node in the heart?

    <p>Acts as a pacemaker for electrical rhythm</p> Signup and view all the answers

    What happens when phase 4 reaches threshold in the action potential of the sinoatrial node?

    <p>Calcium channels open, initiating phase 0.</p> Signup and view all the answers

    What is the duration of phase 4 in the action potential of cardiac autorhythmic cells?

    <p>It is prolonged and uninterrupted.</p> Signup and view all the answers

    What primarily causes the slow depolarization observed in phase 4?

    <p>Simultaneous Na+ and Ca2+ influx</p> Signup and view all the answers

    Which of the following correctly describes the role of Purkinje fibers in the heart?

    <p>They are responsible for rapid conduction of action potentials.</p> Signup and view all the answers

    What is the primary function of Lead I in an ECG?

    <p>To measure the action potentials from right to left</p> Signup and view all the answers

    Which leads define the anterior wall of the heart in a standard ECG?

    <p>V3 and V4</p> Signup and view all the answers

    Which ECG lead configuration is bipolar?

    <p>I, II, III</p> Signup and view all the answers

    What position should a patient be in when recording an ECG?

    <p>Supine</p> Signup and view all the answers

    How many precordial leads are used in a standard ECG setup?

    <p>6</p> Signup and view all the answers

    What type of leads are aVR, aVL, and aVF considered?

    <p>Unipolar augmented limb leads</p> Signup and view all the answers

    Which leads represent the right side of the heart in an ECG?

    <p>aVR</p> Signup and view all the answers

    What does the lead configuration V1 and V2 primarily assess in the heart?

    <p>Septal wall activity</p> Signup and view all the answers

    Study Notes

    Cardiac Action Potential Phases

    • Action potential (AP) may drop to approximately +30 mV before returning to resting potential.
    • Duration of each phase varies and is not clearly defined.
    • Potassium channels open, allowing transient outward potassium current (Ito) which transitions membrane potential from positive to negative.

    Phase 4: Resting Potential

    • Cardiac myocyte remains quiescent with a resting membrane potential around -90 mV, ready for depolarization.
    • Na+/Ca2+ exchanger (INCX) facilitates calcium influx in exchange for sodium efflux, driven by antiporter protein.
    • Inward rectifying potassium current (Ik1) contributes to more negative intracellular potential, allowing K+ outflow at low voltages.

    Phase 0: Rapid Depolarization

    • Fast sodium channels open rapidly, causing a surge of Na+ into the cell, shifting membrane potential from -90 mV to +50 mV.
    • Rapid depolarization reaches approximately +50 mV, immediately followed by K+ activation.
    • Triggered by arrival of action potential from neighboring cells.

    Phase 1: Early Repolarization

    • Transient opening of potassium channels (Ito) occurs quickly, with a change rate up to 250 V/sec within 0.5 msec.
    • Results in an “overshoot” AP around +20 to +50 mV, bringing down potential due to K+ efflux and Na+ channel closure.

    Phase 2: Plateau Phase

    • Characterized by the prolonged opening of calcium channels, maintaining a positive membrane potential.
    • Unique to cardiac AP, unlike neuronal action potentials which lack a plateau phase.

    Phase 3: Repolarization

    • Opening of K+ channels facilitates return to resting membrane potential, triggered until potential stabilizes.

    Autorhythmic Cells

    • Comprise about 1% of cardiac muscle cells, found in the sinoatrial (SA) node and atrioventricular (AV) node.
    • Serve as pacemakers, initiating heartbeat by faster depolarization.
    • Phase 4 exhibits slow depolarization due to a gradual influx of Na+ and Ca2+ until threshold is reached.

    ECG Recording

    • Position patient supine and attach electrodes to chest and lower extremities.
    • Standard ECG has 12 leads:
      • Three standard limb leads (I, II, III)
      • Three augmented limb leads (aVR, aVL, aVF)
      • Six chest leads (V1 through V6).
    • V1 and V2 monitor the septal wall; V3 and V4 observe the anterior wall; V5 and V6 assess the lateral wall.

    Lead Representations

    • Lead I reflects the difference of action potentials from the right to left, indicating the left/lateral wall of the heart.
    • Leads II and III correspond to the inferior wall, while aVR focuses on the right side and aVL on the left side/lateral wall.

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    Description

    Explore the dynamics of action potentials in neuroscience, focusing on the role of potassium channels and their impact on membrane potential. This quiz will help you understand how the transient outward potassium current contributes to the action potential's characteristics.

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