Cardiac Action Potential and Heart Cells
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Questions and Answers

What is the direction of blood flow pumped by the Right Ventricle?

  • To the lungs (correct)
  • To the heart
  • To the rest of the body
  • To the liver
  • What is the ability of cardiac cells to respond to a stimulus?

  • Contractility
  • Excitability (correct)
  • Automaticity
  • Conductivity
  • What occurs when cardiac cells lose their negativity?

  • Relaxation
  • Repolarization
  • Contraction
  • Depolarization (correct)
  • What is the process by which cardiac cells return to their resting state?

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

    What is the phase of cardiac contraction equivalent to?

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

    What is the primary function of the epicardium?

    <p>To provide a protective layer of connective tissue</p> Signup and view all the answers

    What occurs during early ventricular diastole?

    <p>Blood is sucked down from the atria into the ventricles</p> Signup and view all the answers

    What is the term for ventricular contraction?

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

    What is the primary function of the endocardium?

    <p>To line the inside of the heart and protect the valves and chambers</p> Signup and view all the answers

    During which phase of the cardiac cycle does the atria begin to contract?

    <p>Late ventricular diastole</p> Signup and view all the answers

    What is the term for the thin protective coating of the heart?

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

    What is the primary purpose of an action potential in heart cells?

    <p>To propagate a wave of depolarization throughout the heart</p> Signup and view all the answers

    What is the primary ion responsible for depolarization in pacemaker cells?

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

    What is the function of the plateau phase in myocardial cell action potential?

    <p>To prolong the cardiac action potential</p> Signup and view all the answers

    Which type of channels are 'leaky' and maintain the resting potential in myocardial cells?

    <p>Inward Rectifier K Channels</p> Signup and view all the answers

    Which phase of the myocardial cell action potential is characterized by rapid depolarization?

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

    What is the composite representation of action potentials from all cardiac cells?

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

    What is the cardiac action potential composed of?

    <p>A complete cycle of depolarization and repolarization</p> Signup and view all the answers

    What is the function of myocardial cells?

    <p>To contract and relax in response to electrical signals</p> Signup and view all the answers

    What characteristic allows pacemaker cells to depolarize spontaneously?

    <p>The presence of 'leaky K channels'</p> Signup and view all the answers

    Which type of cells is responsible for efficiently conducting electrical signals to distant regions of the heart?

    <p>Electrical conducting cells</p> Signup and view all the answers

    Where are the dominant pacemaker cells located?

    <p>In the upper Right Atrium (SA Node)</p> Signup and view all the answers

    What influences the firing rate of the SA Node?

    <p>The autonomic nervous system and increased demand</p> Signup and view all the answers

    What is the primary function of the Pacemaker Potential in pacemaker cells?

    <p>To begin depolarizing the cell again</p> Signup and view all the answers

    What is the effect of Acetylcholine release on the heart rate?

    <p>It decreases the rate of rise of Phase 4 depolarization</p> Signup and view all the answers

    What is the native pacemaker of the heart?

    <p>Sinoatrial (Sinus) Node</p> Signup and view all the answers

    What is the sequence of contraction in the cardiac conduction system?

    <p>SA Node → Atria → AV Node</p> Signup and view all the answers

    What is the role of 'Backup' Pacemakers in the heart?

    <p>To take over when the SA Node fails or its impulse is blocked</p> Signup and view all the answers

    What is theBundle of His?

    <p>A bundle of fibers that splits into the Left and Right Bundle Branches</p> Signup and view all the answers

    Study Notes

    Cardiac Action Potential

    • A complete cycle of depolarization and repolarization makes up the Cardiac Action Potential.

    Cardiac Cells

    • There are three types of cells in the heart: Pacemaker cells, Electrical conducting cells, and Myocardial cells.
    • Pacemaker cells:
      • Are small, about 5 to 10 μm long.
      • Can depolarize spontaneously over and over again.
      • Have no true resting potential due to “leaky K channels”.
      • Are located in the upper Right Atrium (SA Node).
    • Electrical conducting cells:
      • Carry current rapidly and efficiently to distant regions of the heart.
      • The AV Node is a slow conductor.
      • Atrial conducting systems can vary anatomically, while the ventricular conducting system forms distinct pathways.
    • Myocardial cells:
      • Make up the largest part of heart tissue.
      • Are about 50 to 100 μm long.
      • Contain an abundance of actin and myosin (contractile proteins).
      • Depolarization wave reaching a myocardial cell causes calcium release → cells contract (excitation–contraction coupling).

    Pacemaker Cells

    • The SA Node spontaneously fires 60 to 100 times per minute, and varies based on:
      • Autonomic nervous system (Sympathetic vs. parasympathetic).
      • Increased demand (exercise vs. rest).
    • Autonomic regulation of heartbeat:
      • Vagal Nerve slows HR → ↑Acetylcholine release = ↓ rate of rise of Phase 4 depolarization.
      • Accelerant nerve speeds HR → ↑Norepinephrine release = ↑ rate of rise of the cardiac action potential during phase 0.
      • ↑Epinephrine release = ↑ rate of rise and acetylcholine.

    Cardiac Conduction System

    • The cardiac conduction system consists of:
      • Native/dominant pacemaker: Sinoatrial or Sinus node (60-100 BPM).
      • Ectopic/latent pacemaker: Atrial Pacemaker (60-75 BPM), AV Node (Junctional) (40-60 BPM), Myocardial (Ventricular) cells (30-45 BPM), and Conducting (Purkinje) cells (30-40 BPM).
    • The cardiac conduction system works as follows:
      • SA node → Bachman’s Bundle (depolarization of LA) → SA node → AV node (short delay) → Bundle of His (splits) → L&R Bundle Branches (depolarization of ventricles) → Purkinje System (depolarization of rest of ventricles).

    Cardiac Electrophysiology

    • Physiological properties of myocardial cells:
      • Automaticity: ability to initiate an impulse.
      • Excitability: ability to respond to a stimulus.
      • Conductivity: ability to transmit an impulse.
      • Contractility: ability to respond with pumping action.
    • Cardiac cells are electrically polarized (negatively charged) in the resting state.
    • Depolarization: the loss of negativity in cardiac cells.
    • Repolarization: return to resting polarity (negatively charged).

    Action Potentials

    • An action potential is a brief change in voltage (membrane potential) across the cell membrane of heart cells.
    • Comprised of one complete cycle of depolarization and repolarization.
    • Initiates a wave of depolarization that propagates throughout the heart.
    • ECG is the composite representation of action potentials of all cardiac cells.
    • Phases of action potential:
      • Phase 0: Rapid depolarization.
      • Phase 1: Slight repolarization.
      • Phase 2: Plateau phase.
      • Phase 3: Rapid Repolarization.
      • Phase 4: Diastolic resting membrane potential.

    Pacemaker Cell Action Potential

    • Similar to depolarization in the myocardium, except:
      • Depolarization results from the influx of Calcium (rather than Na).
      • There is no plateau phase (no Phase 1 and 2).

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    Description

    Learn about the cardiac action potential, pacemaker cells, electrical conducting cells, and myocardial cells. Understand the structure and function of different heart cells and their roles in the heart's electrical and contractile functions.

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