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General Properties of Cardiac Muscle

General Properties of Cardiac Muscle. Fig Heart. Fig 10-1. Fig Microscopic Structure of Cardiac Muscle. Fig 9-2. Properties of myocardial cells. Automaticity (Chronotropic property) Conductivity (Dromotropic property) Contractivity (Inotropic property) Excitability (Bathmotropic property).

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General Properties of Cardiac Muscle

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  1. General Properties of Cardiac Muscle

  2. Fig Heart • Fig 10-1

  3. Fig Microscopic Structure of Cardiac Muscle • Fig 9-2

  4. Properties of myocardial cells • Automaticity (Chronotropic property) • Conductivity (Dromotropic property) • Contractivity (Inotropic property) • Excitability (Bathmotropic property)

  5. Fig automaticity • fig 10-2

  6. Automaticity (Chronotropic property) • Pacemaker cell • SA node, AV node and Purkinje fiber • Slow diastolic depolarization • Follower cell • bundle of His, ventricular muscle, et al. • Ion channels • Fast Na+ channel • Slow Ca2+-Na+ channel • K+ channel • Resting membrane potential (RMP) • Maximal diastolic potential (MDP) • Threshold potential (TP)

  7. Fig Stannius ligature • page 5

  8. Regulation of Automaticity • Maximal diastolic potential • Decreased by acetylcohline • Rate of diastolic depolarization • Decreased by acetylcholine • Increased by norepinephrine • Threshold potential

  9. Fig regulation of automaticity • handbook 167

  10. Conductivity(Dromotropic property) • Sinoatrial (SA) node • Internodal tract • Atrioventricular (AV) node • Bundle of His (AV bundle) • Bundle branches (left and right) • Purkinje fiber • Ventricular muscle

  11. Sinoatrial (SA) node • Junction of superior vena cava and right atrium • 8 x 8 x 2 mm3 • Innervations of sympathetic nerve and parasympathetic nerve

  12. Atrioventricular (AV) node • Interatrial septum, near coronary sinus • 22 x 10 x 3 mm3 • AV conduction delay • AN (upper; atrionodal zone) • N (middle zone of nodal cell) • NH (Lower; nodal-His zone)

  13. Table conduction speed • table Ganong 28-1

  14. AV conduction delay • Allows time for the atria to emty their contents into ventricle • Smaller fiber diameter • Less intercalated disc • Poor differentiation • Regulated by sympathetic and parasympathetic nerves (negative and positive dromotropic effect)

  15. Intercalated Disc • Cell membrane seperate but also connect cardiac muscle cells • Gap junction • Low resistance (5 ohm cm2 vs 2000 ohm cm2) • Functional syncytium

  16. Fig functional syncytium • Fig 11

  17. Contractility (Inotropic property) • Ventricle, Ventricular muscle • Correlated to intracellular concentration of Ca2+ • Sympathetic stimulation • Inotropic drugs

  18. Fig inotropic property • Gan 29-8

  19. Excitability (Bathmotropic property) • Full recovery time (FRT) • Absolute refractory period (ARP) • Inactivation of fast Na+ channels • Relative refractory period (RRP) • Part of fast Na+ channels are recovered to resting stage • Supernormal period (SNP) • Most of fast Na+ channels are recovered • Higher membrane potential

  20. Fig excitability • Page 12+13

  21. Fig extrasystolic contraction • page 14

  22. Extrasystolic contraction • Premature contraction • Compensatory period • Extopic focus • Ischemia • Stimulants (Nicotine, Caffeine) • Lack of sleep • Stress, anxiety

  23. Myocardial cells and autonomic nervous system Sympa. Para. Chronotropism (frequency) + - Dromotropism (conduction) + - Inotropism (contractility) + Bathmotropism (excitability) + -

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