Properties of Cardiac muscle Part 2 Dr Arun

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Properties of Cardiac muscle (Part 2) Dr. Arun Goel Associate professor Department of Physiology

Properties of Cardiac muscle (Part 2) Dr. Arun Goel Associate professor Department of Physiology

Properties of the cardiac muscle: I. Excitability II. Rhythmicity III. Conductivity IV. Contractility

Properties of the cardiac muscle: I. Excitability II. Rhythmicity III. Conductivity IV. Contractility

Disorders of conduction and spread of impulse WPW (Wolf-Parkinson-White) syndrome Ectopic pacemakers Extrasystole and

Disorders of conduction and spread of impulse WPW (Wolf-Parkinson-White) syndrome Ectopic pacemakers Extrasystole and compensatory pause

Disorders of conduction and spread of impulse Stannius ligatures in amphibian heart First ligature

Disorders of conduction and spread of impulse Stannius ligatures in amphibian heart First ligature Second ligature

Disorders of conduction and spread of impulse A- V blockage Ventricular escape Stoke Adam

Disorders of conduction and spread of impulse A- V blockage Ventricular escape Stoke Adam Syndrome

Contractility Action potential Increase in intracellular calcium Contraction Excitation-contraction coupling Atrial and ventricular myocytes

Contractility Action potential Increase in intracellular calcium Contraction Excitation-contraction coupling Atrial and ventricular myocytes can contract while pacemaker and conducting system do not Action potential and contraction in ventricle myocyte

Excitation-Contraction Coupling Mechanism by which AP causes myofibrils to contract AP passes over cardiac

Excitation-Contraction Coupling Mechanism by which AP causes myofibrils to contract AP passes over cardiac ms membrane AP spread to interior of cardiac ms along T tubules opening of Ca 2+ channels in sarcolema Ca 2+ diffuses down gradient into cell through T tubules Opening of Ca 2+-release channels in SR Ca 2+ binds to troponin & stimulates contraction

Excitation-Contraction Coupling During Repolarization At the end of plateau of cardiac AP Ca 2+

Excitation-Contraction Coupling During Repolarization At the end of plateau of cardiac AP Ca 2+ is rapidly & actively pumped out via a Na+- Ca 2+- exchanger Cessation of the contraction

Excitation-Contraction Coupling and Relaxation of Cardiac Muscle

Excitation-Contraction Coupling and Relaxation of Cardiac Muscle

Factors affecting myocardium 1. Cardiac innervation 2. Effect of ions concentration in ECF 3.

Factors affecting myocardium 1. Cardiac innervation 2. Effect of ions concentration in ECF 3. Physical factors 4. Blood flow 5. Chemical factors (drugs)

• • Chronotropic Ionotropic Bathmotropic Dromotropic

• • Chronotropic Ionotropic Bathmotropic Dromotropic

Factors affecting myocardium 1. Cardiac innervation 2. Effect of ions concentration in ECF 3.

Factors affecting myocardium 1. Cardiac innervation 2. Effect of ions concentration in ECF 3. Physical factors 4. Blood flow 5. Chemical factors (drugs)

Factors affecting myocardium 6. Mechanical factors: a. b. c. All or none law Staircase

Factors affecting myocardium 6. Mechanical factors: a. b. c. All or none law Staircase phenomenon Starling’s law of the heart

Starling’s law of the heart ■ “Length-tension relationship” ‘Within limits, the greater the initial

Starling’s law of the heart ■ “Length-tension relationship” ‘Within limits, the greater the initial length of the fiber, the stronger will be the force of its contraction; However, overstretching the fiber as in heart failure its power of contractility decreases’ i. e. within limits, the power of contraction is directly proportional to the initial length of the ms ■ Cardiac ms accommodates itself (up to certain limit) to the changes in venous return

Pressure-volume loop

Pressure-volume loop

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