Cardiac Physiology Overview
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Questions and Answers

What causes the pacemaker potential in the SAN during phase 4?

  • Increased influx of Mg2+ ions
  • Increased efflux of Cl- ions
  • K+ influx through leak channels
  • Na influx through funny channels (correct)

    • Which phase of the SAN action potential is characterized by depolarization from -40 mv to +10 mv?

  • Phase 1
  • Phase 0 (correct)
  • Phase 3
  • Phase 2

    • What primarily leads to the repolarization of the SAN during phase 3?

  • Increased Na+ influx
  • Increased K+ efflux (correct)
  • Increased Cl- influx
  • Decreased Ca2+ influx (correct)

    • What effect does sympathetic stimulation have on SAN rhythmicity?

    <p>Increases Na+ permeability</p> Signup and view all the answers

    What is the effect of mild vagal stimulation on sinus rhythm?

    <p>Decreases sinus rhythm to below 75/min</p> Signup and view all the answers

    How does moderate warming affect the rhythmicity of the SAN?

    <p>Increases the slope of pacemaker potential</p> Signup and view all the answers

    Which of the following factors reduces the rhythmicity of the SAN?

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

    What is a positive chronotropic factor?

    <p>Stimulus that increases heart rate</p> Signup and view all the answers

    What is the main origin of rhythmicity in the heart?

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

    Which structure in the heart has the highest intrinsic rhythm rate?

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

    What is the primary purpose of the properties of cardiac muscle such as contractility and excitability?

    <p>To ensure effective pumping of blood</p> Signup and view all the answers

    What is the resting membrane potential (RMP) of the Sinoatrial Node (SAN) cells?

    <p>-55 mv</p> Signup and view all the answers

    Which phase of the action potential in the SAN corresponds to the gradual rise in membrane potential from -55/-60 mv to -40 mv?

    <p>Pacemaker potential</p> Signup and view all the answers

    What characteristic does NOT describe the rhythmicity of the heart?

    <p>It is initiated by the nerves</p> Signup and view all the answers

    What is the resting state of the cardiac muscle often referred to as?

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

    What happens to the SAN's action potential when the Na+ permeability increases?

    <p>Self-excitation occurs</p> Signup and view all the answers

    What is the primary effect of an increase in body temperature on heart rate?

    <p>Increases heart rate by 8-10 beats/minute for each degree Celsius</p> Signup and view all the answers

    Which of the following factors typically decreases cardiac rhythmicity?

    <p>Mild hyperkalemia</p> Signup and view all the answers

    What effect does hypoxia (reduced oxygen) have on cardiac rhythmicity?

    <p>It decreases rhythmicity</p> Signup and view all the answers

    The Faget sign is characterized by which of the following?

    <p>Relative bradycardia in association with fever</p> Signup and view all the answers

    Which ions are critical for normal heart function by affecting the cardiac rhythmicity?

    <p>Sodium, potassium, and calcium ions</p> Signup and view all the answers

    What is the primary role of the sinoatrial node (SAN) in heart function?

    <p>To generate and propagate electrical impulses</p> Signup and view all the answers

    What mechanism does digitalis use to affect heart rhythm?

    <p>Depresses the nodal tissue leading to decreased rhythmicity</p> Signup and view all the answers

    What is the effect of acidosis on the affinity of catecholamines for cardiac receptors?

    <p>Decreases affinity between catecholamines and receptors</p> Signup and view all the answers

    What initiates the action potential in the cardiac impulse transmission process?

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

    What is the velocity of the cardiac impulse transmission in the atria?

    <p>1 m/sec</p> Signup and view all the answers

    Which of the following is NOT a cause of AVN delay?

    <p>Higher number of gap junctions</p> Signup and view all the answers

    What allows sufficient time for the atria to empty their blood into the ventricles?

    <p>AVN delay</p> Signup and view all the answers

    What is the characteristic velocity of the Purkinje system during impulse transmission?

    <p>4 m/sec</p> Signup and view all the answers

    Which factor is NOT associated with the rapid conduction in the Purkinje system?

    <p>Low permeability of gap junctions</p> Signup and view all the answers

    In which direction does the AV bundle conduct impulses?

    <p>From atria to ventricles only</p> Signup and view all the answers

    What is the speed of impulse transmission through ventricular muscle?

    <p>0.3 – 0.5 m/sec</p> Signup and view all the answers

    Study Notes

    Cardiac Physiology Overview

    • The heart's action potential is characterized by three phases:
      • Resting Membrane Potential (RMP): Polarized state before action potential begins.
      • Depolarization: Triggered by Na+ influx.
      • Repolarization: Followed by K+ efflux restoring RMP.

    Properties of Cardiac Muscle

    • Four essential properties for heart function:
      • Rhythmicity: Heart beats regularly; myogenic origin—doesn't require neural initiation.
      • Excitability: Cardiac muscle's response to stimuli.
      • Conductivity: Ability to transmit electrical impulses.
      • Contractility: Ability to contract and pump blood.

    Rhythmicity

    • Defined as the regular beating of the heart.
    • Origin: Myogenic; heart beats before nerve development in a fetus and continues in transplanted hearts.
    • Self-excitation: Natural properties of nodal (SA node, AV node) and conducting fibers (e.g., Purkinje fibers).
    • Heart Rate:
      • SA Node: ~110 beats/min
      • AV Node: ~90 beats/min
      • Bundle Branches: ~45 beats/min
      • Purkinje Fibers: ~35 beats/min
      • Ventricles: ~25 beats/min

    Mechanism of Rhythmicity (SAN Action Potential)

    • Pacemaker Potential (Phase 4):
      • Gradual rise in membrane potential due to Na+ influx and Ca2+ influx.
      • Causes diastolic depolarization.
    • Depolarization (Phase 0):
      • Membrane potential from -40 mV to +10 mV through Ca2+ influx.
    • Repolarization (Phase 3):
      • Ca2+ influx ceases; K+ efflux returns potential to RMP.

    Factors Affecting Rhythmicity

    • Nervous Factors:
      • Sympathetic stimulation increases rhythmicity; vagal stimulation decreases it.
    • Physical Factors:
      • Moderate warming enhances rhythmicity; excessive warming or cooling can reduce it.
    • Chemical Factors:
      • Catecholamines increase; cholinergic drugs and high K+ levels decrease rhythmicity.
      • Blood gas effects: O2 decrease improves rhythmicity; CO2 increase and H+ concentration changes can impair it.
      • Balanced Na+, K+, and Ca2+ ion levels are crucial for rhythmicity.

    Conductivity

    • Defined as the heart's ability to conduct excitation waves.
    • Impulse Transmission:
      • Starts from the SA Node.
      • Travels through atria, AV Node (with a notable delay), Purkinje system, and into the ventricular muscle.

    Phases of Impulse Transmission

    • Through Atria:
      • Action potential travels at approximately 1 m/sec.
    • Through AV Node:
      • Delayed transmission at 0.02-0.05 m/sec; delay allows atrial emptying into ventricles.
    • Through Purkinje System:
      • Rapid conduction at about 4 m/sec; large fibers enhance speed.
    • In Ventricular Muscle:
      • Transmission speed of 0.3-0.5 m/sec.

    Factors Affecting Conductivity

    • Influenced by the same factors that affect rhythmicity.
    • Dromotropism:
      • Positive factors increase conductivity; negative factors decrease it.

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    Cardiac Properties 1 PDF

    Description

    This quiz covers the fundamentals of cardiac physiology, focusing on the action potential and essential properties of cardiac muscle. Understand the phases of the heart’s electrical activity and the significance of rhythmicity, excitability, conductivity, and contractility in heart function.

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