Cardiac Action Potentials and Conduction System
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Questions and Answers

What is the primary event that occurs during the depolarization phase of cardiac action potentials?

  • K+ leak channels become active, allowing K+ to leave the cell
  • Na+ channels open, increasing permeability to Na+ (correct)
  • Ca2+ channels close, decreasing Ca2+ influx
  • K+ channels open, increasing permeability to K+

    • What mechanism causes the initial repolarization during cardiac action potentials?

  • Blockage of K+ channels preventing K+ efflux
  • Increased permeability to intracellular anions
  • Activation of Ca2+ channels allowing influx of Ca2+
  • Inactivation of Na+ channels and opening of K+ channels (correct)

    • What role do the concentration and electrical gradients play during the depolarization phase?

  • They cause a decrease in intracellular cations by actively pumping Na+ out
  • They promote the rapid influx of Na+ into the cell (correct)
  • They drive Na+ out of the cell and K+ into the cell
  • They prevent K+ from leaving the cell, maintaining depolarization

    • What triggers the opening of voltage-gated K+ channels during the repolarization phase?

    <p>The attainment of threshold potential</p> Signup and view all the answers

    What characterizes the inactivation of voltage-gated Na+ channels during cardiac action potentials?

    <p>Their inactivation is time-dependent, not voltage-dependent</p> Signup and view all the answers

    What initiates the cardiac action potential (AP) in the heart?

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

    What is the primary role of the AV node in cardiac conduction?

    <p>To create a delay between atrial and ventricular contractions</p> Signup and view all the answers

    Which components of the conduction system transmit APs to the ventricles?

    <p>Both A and B</p> Signup and view all the answers

    What occurs during the brief pause in the cardiac cycle?

    <p>The AV node slowly propagates the AP</p> Signup and view all the answers

    What characteristic feature ensures the ventricles contract almost simultaneously?

    <p>Rapid conduction through Purkinje fibers and myocytes</p> Signup and view all the answers

    Which of the following is NOT a component of the specialized conduction system of the heart?

    <p>Atrial myocytes</p> Signup and view all the answers

    How does the cardiac conduction system maintain an orderly sequence of heartbeats?

    <p>By providing specific timing between atrial and ventricular contractions</p> Signup and view all the answers

    What happens to the atria during the contraction phase?

    <p>They contract simultaneously, emptying into the ventricles</p> Signup and view all the answers

    What is the primary function of pulmonary circulation?

    <p>Delivery of poorly oxygenated blood to the lungs</p> Signup and view all the answers

    Which sequence correctly describes the pathway of blood in systemic circulation?

    <p>L ventricle → aorta → systemic vessels → vena cava</p> Signup and view all the answers

    What is the role of the right ventricle in the circulatory system?

    <p>Delivers poorly oxygenated blood to the lungs</p> Signup and view all the answers

    What type of receptor do norepinephrine and epinephrine bind to on cardiac muscle cells?

    <p>Beta1-adrenergic receptors</p> Signup and view all the answers

    Which structure receives highly oxygenated blood after it leaves the lungs?

    <p>Left atrium</p> Signup and view all the answers

    Which neurotransmitter is released by the parasympathetic nervous system?

    <p>Acetylcholine (ACh)</p> Signup and view all the answers

    How does systemic circulation differ from pulmonary circulation?

    <p>Systemic circulation transports oxygenated blood to tissues</p> Signup and view all the answers

    What is the role of the sympathetic nervous system in blood pressure regulation?

    <p>Increases heart rate and contractility</p> Signup and view all the answers

    What is the order of blood flow from the right atrium to the lungs?

    <p>Right atrium → right ventricle → pulmonary artery</p> Signup and view all the answers

    In the context of the circulatory system, what does the term 'low pressure circulation' refer to?

    <p>Pulmonary circulation</p> Signup and view all the answers

    Which type of adrenergic receptors are linked to intracellular Gq pathways?

    <p>Alpha1-adrenergic receptors</p> Signup and view all the answers

    Which of the following vessels plays a key role in returning blood to the right atrium?

    <p>Vena cava</p> Signup and view all the answers

    What effect do M2 muscarinic receptors have on cardiac muscle cells?

    <p>Decrease heart rate</p> Signup and view all the answers

    What response occurs when the baroreceptor reflex stimulates an increase in stroke volume (SV)?

    <p>Mean arterial pressure (MAP) will increase</p> Signup and view all the answers

    How do atrial volume receptors indirectly sense changes in blood volume?

    <p>By detecting atrial stretch and distention</p> Signup and view all the answers

    What effect does increased blood volume have on mean arterial pressure (MAP) in the context of the atrial volume receptor reflex?

    <p>Increases MAP and signals a reduction in MAP through reflex mechanisms</p> Signup and view all the answers

    What role does the central nervous system (CNS) play in the atrial volume receptor reflex after detecting increased blood volume?

    <p>Stimulates parasympathetic signaling to decrease MAP</p> Signup and view all the answers

    What occurs during the rapid depolarization phase of the fast response action potential in cardiac muscle?

    <p>There is an increase in ventricular chamber pressure</p> Signup and view all the answers

    Which of the following describes a limitation of the baroreceptor reflex?

    <p>Minimizes deviations from normal but does not return to normal</p> Signup and view all the answers

    Which event signifies the end of diastole in the cardiac cycle?

    <p>Closing of the AV valves</p> Signup and view all the answers

    What happens in the cardiac cycle when the atrium depolarizes?

    <p>Ventricular filling is completed</p> Signup and view all the answers

    What causes the first heart sound (S1) during the cardiac cycle?

    <p>Closing of the AV valve</p> Signup and view all the answers

    In which phase does isovolumetric contraction occur?

    <p>After the AV valve closes and before the aortic valve opens</p> Signup and view all the answers

    Which of the following correctly describes the state of left ventricular pressure during the cardiac cycle?

    <p>It increases significantly during ventricular contraction</p> Signup and view all the answers

    What happens at the start of diastole?

    <p>The ventricular pressure decreases</p> Signup and view all the answers

    What is the sequence of events that occurs when the semilunar valves close?

    <p>End of systole, beginning of diastole</p> Signup and view all the answers

    Study Notes

    Physiology (0603302)

    • Course: Ch.3 Cardiac Physiology
    • Semester: Summer 2023/2024
    • Instructor: Dr. Mohammad A. Abedal-Majed
    • Institution: The University of Jordan, School of Agriculture

    Cardiac Physiology Video Resources

    • Video (327): How does human circulatory system work - 3D animation (YouTube)
    • Video (328): Human Heart Anatomy And Physiology | How Human Heart works? (3D Animation) (YouTube)
    • Video (335): Circulatory System and Pathway of Blood Through the Heart (YouTube)

    Blood Flow

    • Pulmonary circulation (low pressure): poorly oxygenated blood to lungs, then highly oxygenated blood returns to heart
    • Systemic circulation (high pressure): highly oxygenated blood to body tissues, then poorly oxygenated blood returns to the heart

    Vascular System

    • Pump (heart): distributes & collects blood
    • Distributing tubes (arterial system): branching aorta & pulmonary artery, progressively smaller vessels (arteries → arterioles → capillaries)
    • Collecting tubes (venous system): into vena cava & pulmonary veins, vessels join to form larger vessels (capillaries → venules → veins)
    • Exchange system (capillary beds): gas, nutrient, and waste exchanged between blood and tissues

    Cardiac Output

    • Cardiac output = Stroke Volume × Heart Rate
    • Stroke volume = volume of blood pumped by each ventricle per beat (avg. 70 ml/beat)
    • Heart rate = heart beats/min (avg. 70 beats/min)
    • Resting cardiac output ≈ 5 liters/min
    • Exercise cardiac output: increases to 20-25 liters/min

    Heart Valves

    • Atrioventricular valves (AV): between atria and ventricles; open during atrial contraction, close during ventricular contraction (left: mitral; right: tricuspid)
    • Semilunar valves: from ventricles to the aorta and pulmonary artery; open during ventricular contraction, close during ventricular relaxation (left: aortic; right: pulmonic)

    Electrical Activity of Cardiac Muscle Cells

    • Specialized muscle cells in the SA node depolarize spontaneously
    • Action potential propagates through cells via gap junctions
    • Pacemaker cells set the basal heart rate.
    • Motor neurons from the sympathetic and parasympathetic nervous systems modify the basal heart rate.
    • Phases of depolarization and repolarization in atrial and ventricular cells.
    • Conduction through SA node, AV node, bundle, branches and Purkinje fibers.

    Cardiac Action Potentials

    • Relatively long duration (100-250 msec) compared to skeletal muscle action potentials
    • Driven by voltage-gated Na+, K+, and Ca2+ channels.
    • Voltage-gated Ca2+ channels crucial for prolonging the action potential.
    • Different phases of action potential: spontaneous depolarization (phase 0), initial repolarization (phase 1), plateau phase (phase 2), and final repolarization (phase 3), followed by resting membrane potential (phase 4).

    Cardiac Cycle

    • Contraction: ventricular chamber pressure ↑, closing of AV valves, opening of semilunar valves
    • Relaxation: ventricular chamber pressure ↓, closing of semilunar valves, opening of AV valves

    Blood Pressure

    • Circulation driven by pressure to transport gases, nutrients, hormones.
    • Blood pressures are additive when the vessel is below the heart (P + pgh), subtractive when above the heart (↓ pressure in vessels above heart).
    • Systolic pressure (highest pressure in arteries): during ventricular contraction.
    • Diastolic pressure (lowest pressure in arteries): during ventricular relaxation.
    • Pulse pressure: difference between systolic and diastolic pressure.
    • Mean arterial pressure (MAP): average pressure driving blood forward MAP= diastolic pressure + 1/3 pulse pressure
    • Resistance: opposition to blood flow (arterioles have high resistance, veins low). Compliance: ability of vessels to distend.

    Total Peripheral Resistance

    • TPR: (change in pressure)/resistance
    • TPR=aortic pressure/cardiac output
    • Resistance is determined by arteriole diameter.

    Clinical Applications

    • Blood viscosity: higher viscosity (anemia) decreases cardiac output, lower viscosity (polycythemia) increases cardiac output
    • Blood pressure measurements: associated with the closing of heart valves.
    • Electrocardiogram (ECG): graphical tracing of variations in cardiac electrical potentials.

    Blood Pressure Regulation

    • Sympathetic nervous system: norepinephrine/epinephrine ↑ heart rate, contractility, and vasoconstriction. Results in ↑ blood pressure.
    • Parasympathetic nervous system: acetylcholine ↓ heart rate and contractility. Results in ↓ blood pressure
    • Baroreceptor reflex: monitors blood pressure and adjusts heart rate, contractility, and vessel tone to maintain normal blood pressure.
    • Atrial volume receptors: monitors blood volume and regulates fluid balance through release of ADH.

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    Ch.3 Cardiac Physiology Summer 2023/2024 PDF

    Description

    This quiz focuses on the mechanisms and events occurring during cardiac action potentials and the conduction system of the heart. It covers depolarization, repolarization, and the roles of different cardiac structures like the AV node. Test your knowledge on the electrical events that drive heart contractions and how they are coordinated.

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