Excitation Contraction Coupling in Muscle Contraction
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Questions and Answers

What is the primary trigger for the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling?

  • Influx of Na+ ions
  • Opening of long acting type K+ channels
  • Activation of troponin C by ATP
  • Stimulation of ryanodine receptors by Ca2+ (correct)

    • In excitation-contraction coupling, what event allows actin-myosin binding leading to muscle contraction?

  • Binding of Ca2+ to troponin C (correct)
  • Pumping of K+ into sarcoplasmic reticulum
  • Activation of troponin I by Ca2+
  • Diffusion of Na+ to myofilaments

    • Which mechanism is responsible for pumping back released Ca2+ into the sarcoplasmic reticulum during muscle relaxation?

  • Na+/K+ pump
  • Cl-/K+ exchanger
  • Ca2+ ATPase (correct)
  • Ca2+/Cl- symporter

    • According to Frank Starling’s Law, what happens to stroke volume as end-diastolic volume (EDV) increases?

    <p>Stroke volume increases up to a certain limit</p> Signup and view all the answers

    What effect does heart failure have on the relationship between end-diastolic volume (EDV) and stroke volume (SV)?

    <p>Shifts the relationship to the right</p> Signup and view all the answers

    Which of the following statements best explains why the V/Q ratio at the top of the lung is infinity?

    <p>Blood flow is least but ventilation is most.</p> Signup and view all the answers

    In the context of the text, what factor determines the stroke volume (SV)?

    <p>End-diastolic volume (EDV)</p> Signup and view all the answers

    According to Frank Starling's Law, what happens to stroke volume as end-diastolic volume (EDV) increases?

    <p>SV increases up to a certain limit.</p> Signup and view all the answers

    Which condition shifts the curve in heart failure according to the text?

    <p>Pulmonary capillary congestion</p> Signup and view all the answers

    What causes Ventilation Perfusion Matching at the bottom of the lung according to the text?

    <p>Accumulation of CO2 in blood causes pulmonary constriction.</p> Signup and view all the answers

    What is the volume of air that remains in the lungs even after a maximal expiration?

    <p>1000 ml</p> Signup and view all the answers

    Which lung volume measurement represents the maximum volume of air that can be inspired at the end of a normal quiet expiration?

    <p>Inspiratory capacity (IC)</p> Signup and view all the answers

    Which lung volume measurement represents the total volume of air that the lungs can hold?

    <p>Total lung capacity (TLC)</p> Signup and view all the answers

    What effect does stimulation of sympathetic nerves have on the heart muscle?

    <p>Increases the force of contraction</p> Signup and view all the answers

    What is the purpose of bronchodilators like B2 agonists and anticholinergics in managing shortness of breath?

    <p>Relieve airway constriction</p> Signup and view all the answers

    In spirometry, what does FEV1/FVC ratio greater than 75% indicate?

    <p>Normal or increased in restrictive disease</p> Signup and view all the answers

    What is the impact of vagal stimulation on the heart?

    <p>Primarily affects heart rate rather than contractility</p> Signup and view all the answers

    Which arrhythmia involves chaotic and disorganized atrial activity resulting in an irregular heartbeat?

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

    What does the absence of a P wave and presence of an abnormal F wave on an ECG indicate?

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

    When ventricular rates are found to be less than 60 bpm, what condition should be considered due to potential AV conduction disease?

    <p>Sinus Bradycardia</p> Signup and view all the answers

    What is the main function of desmosomes within intercalated discs?

    <p>Allowing transmission of tension between adjacent cardiac cells</p> Signup and view all the answers

    What is the contractile unit of muscles known as?

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

    What triggers muscle tension production in sarcomeres?

    <p>Sliding of myosin filaments on actin filaments</p> Signup and view all the answers

    During which phase of the cardiac action potential does the cell become positive?

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

    What happens during the absolute refractory period in cardiac myocytes?

    <p>Generation of action potential is impossible</p> Signup and view all the answers

    In atrial fibrillation, which management approach focuses on restoring sinus rhythm with pharmacologic conversion or electrical cardioversion?

    <p>Rhythm control</p> Signup and view all the answers

    Which condition associated with atrial fibrillation requires long-term oral anticoagulation for stroke prevention?

    <p>Valvular disease</p> Signup and view all the answers

    Among the listed antiarrhythmic drugs, which one primarily works by reducing the Na+ channel current?

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

    What is the primary approach in atrial flutter management when the focus is on accepting AF but controlling the ventricular rate?

    <p>Digoxin administration</p> Signup and view all the answers

    Which of the following conditions contributes to an increased risk of thromboembolic stroke in atrial fibrillation based on the CHA2DS2VASc score?

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

    What is the primary function of the ventilatory pump in maintaining normal respiration?

    <p>Assisting in breathing</p> Signup and view all the answers

    Which receptors are responsible for guarding against hyperinflation during respiration?

    <p>Stretch receptors on bronchi walls</p> Signup and view all the answers

    What stimulates Juxtapulmonary J receptors to cause rapid, shallow breathing?

    <p>Capillary congestion</p> Signup and view all the answers

    Which brain center is primarily responsible for generating the respiratory rhythm?

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

    In spirometry, which lung volume represents the maximum amount of air that can be forcefully exhaled after a maximum inhalation?

    <p>Vital capacity</p> Signup and view all the answers

    What is the term for the increased ventilatory rate caused by decreased blood pressure?

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

    How do the accessory muscles of inspiration differ from major inspiratory muscles like the diaphragm?

    <p>They contract mainly during forceful inspiration.</p> Signup and view all the answers

    What condition may lead to an increased importance of juxtapulmonary J receptors?

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

    How do baroreceptors influence respiration rate?

    <p>Increase ventilatory rate with decreased BP.</p> Signup and view all the answers

    What is the primary neurotransmitter released from sympathetic nerves to the ventricular muscle?

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

    What effect does vagal stimulation have on the heart?

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

    What is the term that describes the extra volume of air that can be maximally inspired over and above the typical resting tidal volume?

    <p>Inspiratory reserve volume (IRV)</p> Signup and view all the answers

    Which condition may require a pacemaker due to a coinciding period of fast ventricular rate?

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

    Which lung volume measurement represents the volume of air in the lungs at the end of normal passive expiration?

    <p>Residual volume (RV)</p> Signup and view all the answers

    What abnormality can be observed on an ECG in atrial fibrillation?

    <p>Absence of P wave</p> Signup and view all the answers

    What condition usually benefits from diuretics in terms of managing shortness of breath?

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

    What is the effect of too fast heart rate on systole and diastole?

    <p>Shortens both systole and diastole</p> Signup and view all the answers

    What term refers to the maximum volume of air that can be moved out during a single breath following a maximal inspiration?

    <p>Vital capacity (VC)</p> Signup and view all the answers

    Which lung volume measurement represents the maximum volume of air that the lungs can hold?

    <p>Total lung capacity (TLC)</p> Signup and view all the answers

    What is the formula for pulmonary ventilation?

    <p>Tidal Volume x Respiratory Rate</p> Signup and view all the answers

    How does accumulation of CO2 in blood affect the lungs?

    <p>Leads to pulmonary constriction</p> Signup and view all the answers

    What determines the Stroke Volume (SV) in the heart?

    <p>End-Diastolic Volume (EDV)</p> Signup and view all the answers

    How does Frank Starling's Law relate EDV and SV in the heart?

    <p>Greater EDV leads to greater SV up to a certain limit</p> Signup and view all the answers

    How does cardiac output affect respiration?

    <p>Affects oxygen and carbon dioxide exchange in the lungs</p> Signup and view all the answers

    What stimulates the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling?

    <p>Stimulation of ryanodine receptors by Ca2+ from the extracellular fluid</p> Signup and view all the answers

    What contributes to an increased risk of thromboembolic stroke in atrial fibrillation according to the CHA2DS2VASc score?

    <p>Co-morbidities like hypertension and heart failure</p> Signup and view all the answers

    What is the effect of vagal stimulation on the heart muscle?

    <p>Decreased force of contraction</p> Signup and view all the answers

    How does heart failure affect the relationship between end-diastolic volume (EDV) and stroke volume (SV)?

    <p>Reduces SV at all levels of EDV</p> Signup and view all the answers

    What triggers muscle tension production in sarcomeres?

    <p>Binding of Ca2+ to troponin C</p> Signup and view all the answers

    Which type of atrial fibrillation lasts greater than 48 hours but can still be converted to normal sinus rhythm?

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

    In atrial fibrillation, what effect does decreased filling times have on cardiac output?

    <p>Reduced CO</p> Signup and view all the answers

    Which pharmacologic agent is primarily used for rhythm control in managing atrial fibrillation?

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

    Which class of antiarrhythmic drugs prolongs the action potential and can be used in atrial fibrillation management?

    <p>Class 3: Action potential prolongation</p> Signup and view all the answers

    In atrial flutter, where is the macro reentrant circuit typically confined?

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

    What is the primary purpose of desmosomes within intercalated discs in cardiac cells?

    <p>Provide mechanical adhesion between adjacent cardiac cells</p> Signup and view all the answers

    During muscle contraction, what is the main factor responsible for producing muscle tension?

    <p>Sliding of actin filaments on myosin filaments</p> Signup and view all the answers

    What ions are involved in the depolarization phase (Phase 0) of cardiac myocytes?

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

    What event marks the beginning of early repolarization (Phase 1) in cardiac myocytes?

    <p>Opening of K+ channels for efflux</p> Signup and view all the answers

    What effect does an increase in intracellular Na+ levels have on the excitability of cardiac myocytes?

    <p>Decreases the ability to generate action potentials</p> Signup and view all the answers

    What is the primary role of the ventilatory pump in maintaining normal respiration?

    <p>Contraction of respiratory muscles to facilitate breathing</p> Signup and view all the answers

    Which receptors are responsible for causing rapid, shallow breathing when stimulated by capillary congestion or pulmonary emboli?

    <p>Juxtapulmonary J receptors</p> Signup and view all the answers

    What is the major muscle responsible for active inspiration during normal respiration?

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

    Which of the following influences the respiratory rhythm but does not generate it directly?

    <p>Higher brain centres</p> Signup and view all the answers

    Which condition may lead to increased significance of juxtapulmonary J receptors in respiration?

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

    What happens when baroreceptors detect decreased blood pressure concerning respiratory rate?

    <p>They stimulate rapid breathing</p> Signup and view all the answers

    Which muscles serve as accessory muscles of inspiration, particularly during forceful breathing?

    <p><strong>Sternocleidomastoid</strong>, scalene, pectoral muscles</p> Signup and view all the answers

    What is the primary effect of stimulating sympathetic nerves on the heart?

    <p>Positive inotropic effect</p> Signup and view all the answers

    In atrial fibrillation, what ECG abnormality is typically observed?

    <p>Irregularly irregular rhythm</p> Signup and view all the answers

    What is the primary impact of vagal stimulation on the heart?

    <p>Rate regulation</p> Signup and view all the answers

    How does excessive heart rate affect systole and diastole?

    <p>Shortens both systole and diastole</p> Signup and view all the answers

    Which neurotransmitter is primarily released from sympathetic nerves to the ventricular muscle?

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

    What is the primary function of desmosomes within intercalated discs in cardiac cells?

    <p>Provide mechanical adhesion between adjacent cardiac cells</p> Signup and view all the answers

    What initiates the process of muscle tension production in sarcomeres?

    <p>ATP interaction with actin and myosin filaments</p> Signup and view all the answers

    During which phase of the cardiac action potential does the cell become positive?

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

    What is the primary trigger for the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling?

    <p>Long acting type Ca2+ channel opening</p> Signup and view all the answers

    What plays a crucial role in preventing heart spasm through refractory periods?

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

    What is the main difference between paroxysmal and persistent atrial fibrillation?

    <p>Duration of episodes</p> Signup and view all the answers

    Which factor is NOT associated with an increased risk of thromboembolic stroke in atrial fibrillation?

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

    What is the primary purpose of rate control management in atrial fibrillation?

    <p>Control ventricular rate</p> Signup and view all the answers

    Which antiarrhythmic drug class primarily works by reducing the Na+ channel current?

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

    What differentiates atrial flutter from atrial fibrillation?

    <p>Location of reentrant circuit</p> Signup and view all the answers

    What is the term for the volume of air in the lungs at the end of normal passive expiration?

    <p>Functional residual capacity</p> Signup and view all the answers

    Which lung volume measurement represents the maximum air that can be inspired at the end of a normal quiet expiration?

    <p>Inspiratory capacity</p> Signup and view all the answers

    What does Forced Expiratory Volume in one second (FEV1) measure?

    <p>Volume of air that can be expired during the first second of expiration</p> Signup and view all the answers

    Which lung volume is calculated by adding Inspiratory reserve volume, Tidal volume, and Expiratory reserve volume?

    <p>Vital capacity</p> Signup and view all the answers

    What is the maximum volume of air that can be moved out during a single breath following a maximal inspiration?

    <p>Vital capacity</p> Signup and view all the answers

    What stimulates the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling?

    <p>Activation of ryanodine receptors</p> Signup and view all the answers

    What is the primary neurotransmitter released from parasympathetic nerves to the ventricular muscle?

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

    Which ion is primarily involved in the depolarization phase (Phase 0) of cardiac myocytes?

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

    How does heart failure affect the relationship between end-diastolic volume (EDV) and stroke volume (SV)?

    <p>It increases EDV and decreases SV</p> Signup and view all the answers

    What is responsible for pumping back released Ca2+ into the sarcoplasmic reticulum during muscle relaxation?

    <p>Ca2+ ATPase pump</p> Signup and view all the answers

    What happens at the top of the lung in terms of ventilation and blood flow?

    <p>Ventilation exceeds blood flow</p> Signup and view all the answers

    How does accumulation of oxygen affect pulmonary vasculature?

    <p>Results in pulmonary vasodilation</p> Signup and view all the answers

    What effect does accumulation of CO2 in blood have on the lungs?

    <p>Results in pulmonary constriction</p> Signup and view all the answers

    How does stroke volume change with increased end-diastolic volume (EDV) according to Frank Starling's Law?

    <p>Increase up to a certain limit</p> Signup and view all the answers

    What effect does heart failure have on the relationship between end-diastolic volume (EDV) and stroke volume (SV)?

    <p>Shifts the curve to the right</p> Signup and view all the answers

    What is the primary factor responsible for dynamic airway compression during expiration?

    <p>Contraction of abdominal muscles</p> Signup and view all the answers

    Which muscle group primarily lifts the ribs and sternum outwards during inspiration?

    <p>External intercostal muscles</p> Signup and view all the answers

    Intrapleural pressure plays a crucial role in lung expansion. What effect does a loss of transmural pressure gradient have on the lungs?

    <p>Decreases lung compliance</p> Signup and view all the answers

    What is a common consequence of decreased chest wall compliance such as in individuals with kyphoscoliosis?

    <p>Impaired gas exchange in the lungs</p> Signup and view all the answers

    Study Notes

    Respiratory System

    • Average tidal volume is 500 ml
    • Inspiratory reserve volume (IRV) is 3000 ml
    • Inspiratory capacity (IC) is 3500 ml
    • Expiratory reserve volume (ERV) is 1000 ml
    • Residual volume (RV) is 1200 ml
    • Functional residual capacity (FRC) is 2200 ml
    • Vital capacity (VC) is 4500 ml
    • Total lung capacity (TLC) is 5700 ml
    • Forced expiratory volume in one second (FEV1) is the volume of air that can be expired during the first second of expiration

    Management of Shortness of Breath

    • Correctly position patient
    • O2 therapy
    • Bronchodilators (B2 agonists and anticholinergics) for those with obstructive lung disease like asthma/COPD
    • Patients with pulmonary oedema usually benefit from diuretics
    • Treat the underlying cause of SOB
    • Lifestyle modifications/palliative care

    Cardiac System

    • Cardiac muscle is striated due to regular arrangement of contractile proteins
    • Cardiac myocytes are electrically coupled by gap junctions
    • Heart failure is a syndrome that can result from structural or functional cardiac disorders that impair the pumping ability of the heart
    • Left heart failure (LHF) is caused by pulmonary capillary congestion/pulmonary oedema

    Force Generation by the Heart

    • Cardiac myocytes have excitability
    • Conduction in cardiac myocytes involves:
      • Phase 0: depolarization
      • Phase 1: early repolarization
      • Phase 2: plateau phase
      • Phase 3: repolarization
      • Phase 4: resting phase

    Cardiac Arrhythmias

    • Atrial fibrillation: chaotic and disorganized atrial activity resulting in an irregular heartbeat
      • ECG: P wave absent, abnormal F wave present, irregularly irregular rhythm
      • May be symptomatic (palpitations, chest pain, dyspnoea, sweaty, fatigue, syncope) or asymptomatic
      • Ventricular rates <60 bpm suggest AV conduction disease thus caution with anti-arrhythmic drugs and rate controlling drugs + may require permanent pacing!

    Cardiovascular Control

    • Intrinsic control:
      • Stroke volume changed depending on diastolic length of myocardial fibres
      • Frank Starling's Law states that the more the EDV, the higher the amount of blood ejected will be, hence the greater the SV will get (but only up to a certain limit!)
    • Extrinsic control:
      • Nerves and hormones
      • Ventricular muscle is supplied by sympathetic nerve fibres, thus neurotransmitter is Noradrenaline
      • Stimulation of sympathetic nerves increases the force of contraction = +ve inotropic effect
      • Stimulation of sympathetic nerves to the heart also causes a positive chronotropic effect (HR)

    Ventilation

    • Pulmonary ventilation = Tidal Volume x Respiratory Rate = 6L/min
    • Alveolar ventilation = Tidal volume - anatomical dead space x Respiratory rate 4.2L/min
    • Ventilation Perfusion Ratio:
      • At the top of the lung, blood flow is least but ventilation is most, hence VQ ratio is = infinity
      • At the bottom, blood flow is most but ventilation is least, hence VQ ratio is almost 0### Shortness of Breath
    • Anaemia is not usually a cause for shortness of breath because temporary increase in cardiac output acts as a compensatory mechanism, thus arterial PO2 sensed by chemoreceptors is normal.

    Lung Volumes

    • Tidal volume (TV): 500 ml (volume of air entering or leaving lungs during a single breath)
    • Inspiratory reserve volume (IRV): 3000 ml (extra volume of air that can be maximally inspired over and above the typical resting tidal volume)
    • Inspiratory capacity (IC): 3500 ml (maximum volume of air that can be inspired at the end of a normal quiet expiration)
    • Expiratory reserve volume (ERV): 1000 ml (extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume)
    • Residual volume (RV): 1200 ml (minimum volume of air remaining in the lungs even after a maximal expiration)
    • Functional residual capacity (FRC): 2200 ml (volume of air in lungs at end of normal passive expiration)
    • Vital capacity (VC): 4500 ml (maximum volume of air that can be moved out during a single breath following a maximal inspiration)
    • Total lung capacity (TLC): 5700 ml (maximum volume of air that the lungs can hold)
    • Forced expiratory volume in one second (FEV1): dynamic volume (volume of air that can be expired during the first second of expiration in an FVC determination)
    • FEV1%: FEV1/FVC ratio (normal >75%)

    Management of Shortness of Breath

    • Correctly position patient
    • O2 therapy
    • Bronchodilators (B2 agonists and anticholinergics) for those with obstructive lung disease like asthma / COPD
    • Patients with pulmonary oedema usually benefit from diuretics
    • Treat the underlying cause of SOB
    • Lifestyle modifications / palliative care

    Force Generation by the Heart

    • Cardiac muscle is striated due to regular arrangement of contractile proteins
    • Cardiac myocytes are electrically coupled by gap junctions
    • Action potential duration: 150ms
    • Excitation Contraction Coupling: opening of long acting type Ca2+ channels in Phase 2 of the action potential allows the influx of Ca2+ from ECF
    • Release of Ca2+ from sarcoplasmic reticulum, then diffusion of Ca2+ to myofilaments
    • Binding of Ca2+ to troponin C exposes cross-bridge binding site, allowing actin-myosin binding and triggering sliding, thus contraction

    Cardiac Output and Stroke Volume

    • CO = SV * HR
    • SV = EDV - ESV
    • Stroke volume changed depending on diastolic length of myocardial fibres
    • EDV determined by venous return to heart
    • Frank Starling’s Law: the more the EDV, the higher the amount of blood ejected will be, hence the greater the SV will get (but only up to a certain limit!)

    Cardiac Arrhythmias

    • Atrial Fibrillation: most common arrhythmia, may be symptomatic (palpitations, chest pain, dyspnoea, sweaty, fatigue, syncope) or asymptomatic
    • Chaotic and disorganised atrial activity resulting in an irregular heartbeat
    • ECG: P wave absent, abnormal F wave present, irregularly irregular rhythm

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    PHYSIOLOGY.docx

    Description

    Learn about the process of excitation-contraction coupling in muscle contraction, involving the opening of long-acting Ca2+ channels, stimulation of ryanodine receptors, release of Ca2+ from the sarcoplasmic reticulum, and binding to troponin C to enable actin-myosin interactions.

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