Excitation & Conduction in the Heart
30 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which autonomic nervous system branch is primarily active at rest?

  • Parasympathetic NS (correct)
  • Central nervous system
  • Peripheral nervous system
  • Sympathetic NS

    • What is the role of the sympathetic nervous system during exercise?

  • Enhances immune response
  • Inhibits digestion (correct)
  • Increases heart rate (correct)
  • Promotes relaxation

    • What ions are specifically mentioned in relation to fiber membrane permeability?

  • Cl- and H+
  • Li+ and Ba++
  • K+ and Mg++
  • Na+ and Ca++ (correct)

    • During both rest and exercise, which autonomic nervous system works but is not dominant?

    <p>Sympathetic nervous system</p> Signup and view all the answers

    Which statement accurately describes the function of the parasympathetic nervous system?

    <p>Stimulates digestion</p> Signup and view all the answers

    What primarily causes depolarization in cardiac cells?

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

    What is the normal discharge rate of the S-A node in times/min?

    <p>70 to 80</p> Signup and view all the answers

    Which cardiac structure has the lowest spontaneous discharge rate?

    <p>Purkinje fibers</p> Signup and view all the answers

    Which of the following cardiac structures can produce impulses by themselves?

    <p>S-A node, A-V node, and Purkinje fibers</p> Signup and view all the answers

    What is the normal discharge rate range of the A-V node in times/min?

    <p>40 to 60</p> Signup and view all the answers

    What occurs after the slow sodium-calcium channel closes?

    <p>The potassium channel opens for repolarization.</p> Signup and view all the answers

    What is the effect of the potassium channel opening?

    <p>It facilitates hyperpolarization.</p> Signup and view all the answers

    What is the time frame mentioned for the closure of the slow sodium-calcium channel?

    <p>100-150 milliseconds</p> Signup and view all the answers

    What happens to the membrane potential during hyperpolarization?

    <p>It falls below the resting membrane potential.</p> Signup and view all the answers

    What ion flux primarily contributes to repolarization following the closure of the sodium-calcium channel?

    <p>Potassium efflux</p> Signup and view all the answers

    What causes the sinus nodal fibers to not remain depolarized continuously?

    <p>Inactivation of Na+ - Ca++ channels</p> Signup and view all the answers

    How long do Na+ - Ca++ channels remain open before inactivation occurs?

    <p>100 - 150 ms</p> Signup and view all the answers

    What happens to the Na+ - Ca++ channels after they open?

    <p>They inactivate and close</p> Signup and view all the answers

    What is the result of the inactivation of Na+ - Ca++ channels in the sinus nodal fibers?

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

    Which of the following ions is primarily involved in the function of sinus nodal fibers?

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

    What is the typical range of resting membrane potential for ventricular muscle fibers?

    <p>-85 to -95</p> Signup and view all the answers

    What is the effect of atrioventricular block on heart rate?

    <p>Decreased heart rate due to slowed impulses</p> Signup and view all the answers

    Which structure in the conduction system of the heart is known for having the slowest conduction velocity?

    <p>AV nodal fibers</p> Signup and view all the answers

    For a patient with purkinje fiber rhythm, what is the typical heart rate experienced?

    <p>40-60 beats per minute</p> Signup and view all the answers

    Which statement is true regarding the electrical activity in the heart?

    <p>Ventricular muscle fibers have a less negative resting potential than Purkinje fibers</p> Signup and view all the answers

    What is the total time required for the excitation of the ventricles?

    <p>0.06 seconds</p> Signup and view all the answers

    How long does the transmission from the bundle branches to the Purkinje fibers take?

    <p>0.03 seconds</p> Signup and view all the answers

    What is the significance of the rapid conduction of action potentials throughout the ventricles?

    <p>It allows efficient contraction and ejection of blood.</p> Signup and view all the answers

    What is the duration from the endocardial surface to the epicardial surface in the context of ventricular excitation?

    <p>0.03 seconds</p> Signup and view all the answers

    Which of the following components contribute to the total excitation time of the ventricles?

    <p>Transmission from endocardial surface to epicardial surface</p> Signup and view all the answers

    Study Notes

    Excitation & Conduction

    • The heart has a specialized excitatory and conductive system composed of specialized cardiac muscles
    • This system's function is to generate and conduct rhythmical electrical impulses that initiate heart muscle contraction
    • The system controls conduction of impulses from one part of the heart to another
    • This coordinated action ensures excitation throughout all heart muscle sections (atria and ventricles)

    Learning Objectives

    • Students should be able to describe the ion currents in different phases of pacemaker cell and ventricular muscle cell action potentials.
    • Students should know the factors contributing to the longer duration of cardiac action potentials.
    • They should be able to outline the normal sequence of depolarization in the heart.
    • Students need to understand the role of specialized cells in conduction. The effects of conduction failures in different areas should be explained.
    • The function of the AV node as the only electrical pathway between atria and ventricles should be described. The functional significance of a slow conduction rate through the AV node should be analyzed.
    • The role of the SA node as the cardiac pacemaker in normal situations should be understood.
    • The relationship between action potentials and mechanical activity in cardiac and skeletal muscle fibers, as well as why tetanic contractions don't happen in a healthy heart, should be explained.
    • Students need to understand how the sympathetic and parasympathetic nervous systems influence cardiac function. The dominant autonomic nervous system branches at rest and during exercise should be identified.

    Specialized Excitatory & Conductive System

    • The sinus node (sinoatrial node) is the primary pacemaker
    • It generates normal rhythmical impulses
    • Located in the upper wall of the right atrium behind the superior vena cava opening
    • Internodal pathways carry impulses from the SA node to the AV node (interconnecting fibers)
    • The AV node delays impulses from atria before passing them to ventricles- crucial for efficient heart function.
    • Located in the posterior wall of the right atrium
    • The A-V bundle conducts impulses from atria to ventricles, insulated from the atria by fibrous tissue
    • Right & Left bundle branches of Purkinje fibers conduct impulses to all parts of the ventricles. This ensures their rapid activation

    Functional relevance of slow conduction through AVN

    • The AV node contains fewer gap junctions between cells compared to other structures in the cardiac conduction system.
    • This decreased gap junction presence leads to slower impulse transmission.
    • The delay allows atria to completely empty their blood into the ventricles before ventricular contraction begins.
    • Reduced conduction velocity in the AV node results in reduced ventricular filling, stroke volume, & cardiac output

    Action Potential of cardiac muscles

    • Depolarization: rapid influx of Na+ ions leads to a rise in membrane potential
    • Plateau phase: sustained depolarization due to opening of slow Ca++ channels and delayed K+ closing. Maintains the contraction.
    • Repolarization: efflux of K+ ions restores the resting membrane potential.
    • The action potential of cardiac muscles lasts longer than that of skeletal muscles to ensure prolonged contraction, essential for cardiac function

    Causes of plateau

    • Slow, prolonged opening of the slow Na+/Ca++ channels.
    • Decreased permeability of K+ channels. Results in increased Ca++ influx maintaining the plateau
    • The return of the MP is delayed
    • This maintains the plateau for a longer time.

    Advantages of the long plateau

    • Prolonged ventricular contraction in comparison to skeletal muscle (15 times longer)
    • Ca++ influx during contraction, making cardiac muscle contractions stronger
    • Delay in repolarization results in an absolute refractory period (necessary to prevent tetanic contractions)

    Con...

    • Prolonged refractory period in cardiac muscle, shielding the heart from rapid re-excitation.
    • So heart muscle cannot exhibit tetanus during high-frequency stimulation. Implies the necessity of relaxations for efficient filling.
    • Allows sufficient ventricular relaxation time for the ventricles to fill with blood efficiently.

    Cardiac Pacemaker (S-A node)

    • The SA node is the heart's primary pacemaker (70-80 beats/min under normal circumstances).
    • The SA node initiates the heart's rhythmic electrical impulses, initiating atrial and ventricular contraction and the heartbeat.
    • Other latent pacemakers like the AV node and the Purkinje fibers (15 to 40 beats/min) can act as backup pacemakers if the SA node fails

    Impulse transmission through ventricles

    • Special Purkinje fibers carry impulses from the AV node to the ventricles
    • Ventricular muscle fibers are large.
    • Extremely high level of permeability of gap junctions in these fibers.
    • This enables rapid impulse transmission to facilitate synchronized ventricular contraction.
    • The impulse through the bundle branches in the ventricular septum, and Purkinje fiber terminals is 0.03 seconds

    Con...

    • Transmission from endocardial surface to epicardial surface takes 0.03 seconds
    • The total duration from the initial bundle branches to the end of ventricular muscle fibers is about 0.06 seconds.
    • Rapid conduction of the action potential throughout the ventricles ensures efficient contraction and blood ejection.

    Velocity of transmission

    • In the specialized fibers(Purkinje fibers) the Velocity of transmission: ranges from 1.5 - to 4.0 m/sec.

    Influence of vagal (parasympathetic) stimulation and sympathetic stimulation

    • Vagus nerve stimulation (parasympathetic) decreases the conduction rate (and heart rate) by increasing K+ efflux, leading to hyperpolarization of the heart's pacemaker cells.
    • Sympathetic stimulation increases the conduction rate (and heart rate) as it increases the rate of depolarization in pacemaker cells due to increased Na+ & Ca++ influx into cells.

    Significance of the Heart's long plateau

    • Prolonged duration of the cardiac action potential is essential for a sustained cardiac muscle contraction, preventing tetanus-like sustained contractions.
    • It allows time for the ventricular filling before ventricular contraction begins.

    Relationship between Action Potential (AP) & mechanical activity in skeletal and cardiac muscle

    • In skeletal muscle, the refractory period is short. Thus, it can sum APs and contractions leading to tetanus if repeatedly stimulated.
    • In cardiac muscle, the refractory period is longer; hence, summation of APs and contractions isn't possible and thus tetanus can't occur. This prevents uncontrolled contractions and ensures smooth, coordinated pumping action.

    Consequences of conduction failure

    • In specialized cells of the conduction pathway, if there's dysfunction, it can lead to an irregular heartbeat.
    • A faster pacemaker elsewhere in the heart takes over if the SA node malfunctions.
    • In a condition called AV block, the upper chambers (atria) beat at a normal rate while the lower chambers (ventricles) beat less frequently, or not at all – in a less-coordinated manner.

    Con...

    • Blockage of impulse transmission from SA node to other components of the heart leads to the establishment of a new pacemaker in the AV node, or penetrating portions of the AV bundle.
    • Failure to transmit impulses in the conduction system can result in an abnormal heart rhythm (arrhythmia). This means the heart doesn't beat in a coordinated or predictable way – it beats too slowly, too quickly, or in an irregular rhythm.
    • Ventricular escape occurs if the primary pacemaker fails, and Purkinje fibers become the new pacemaker at a slower rate.

    MCQ

    • The slowest discharge rate occurs in the AV nodal fibers, followed by Purkinje fibers, and the fastest in the sinus nodal fibers.
    • The resting membrane potential of ventricular muscle fibers is between -75 mV and -85 mV

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Excitation & Conduction تفريغ PDF

    Description

    This quiz covers the heart's specialized excitatory and conductive system, highlighting the functions of cardiac muscles in generating and conducting electrical impulses. Students will explore the action potentials of pacemaker and ventricular cells, the sequence of depolarization, and the importance of the AV node in conduction. Prepare to deepen your understanding of cardiac physiology!

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser