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Cardiac conducting system Anatomy and Physiology

Cardiac conducting system Anatomy and Physiology. QUIZ. 1. Overview. Label the diagram. c). a). d). e). b). f). 2. Membrane potentials 1. The graph shows the changing membrane potentials for a sinus nodal fiber and a muscle fibre. Which is which?. a). b).

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Cardiac conducting system Anatomy and Physiology

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  1. Cardiac conducting systemAnatomy and Physiology QUIZ

  2. 1. Overview Label the diagram. c) a) d) e) b) f)

  3. 2. Membrane potentials 1 The graph shows the changing membrane potentials for a sinus nodal fiber and a muscle fibre.Which is which? a) b)

  4. 2. Membrane potential timing – extra info

  5. 3. Membrane potentials 2 Where on the Y-axis is the zero millivolt level? A B C D E

  6. 4. Pacemaker membrane potential Identify the currents d) e) c) a) b)

  7. 5. Ectopic membrane potential Identify the currents: ICaL, IK, IK1, INa, Ito c) d) b) e) a)

  8. 6. Histology Match the labels a) Endocardium b) Myocardium c) Bundle Branch fibres d) Purkinje fibres H&E/Elastin x400 H&E x150 ? ? ? ? ?

  9. 6. Histology explained • shows the left branch bundle of conducting fibres in the interventricular septum beneath the endocardium. At this level the conducting fibres are separated from the myocardial fibres by a layer of fibrous tissue. The conducting fibres are specialised cardiac muscle fibres, and contain few myofibrils, mainly located beneath the cell membrane, but abundant glycogen granules and mitochondria. This makes these fibres paler staining than normal myocardial fibres by most stains. (b) shows the Purkinje fibresbeneath the thin endocardium. These fibres are larger than cardiac muscle fibres and have a pale staining central area with most of the red-staining myofibrils around the periphery of the cell. Purkinje and other conducting fibres have no T tubule system, and connect with each other by desmosomes and gap junctions rather than intercalated discs.

  10. 7. Propagation of cardiac impulse In what order does the impulse activate the labelled parts? Bonus points – give an expected time in seconds for the impulse to reach each part. ? ? ? ? ? ? ? ? ? ? ?

  11. 8. Easy multi-choice In a non-pathological heart, does a particular cross-section of the ventricle wall depolarize: A. Outer to inner B. Inner to outer C. All at once D. Middle to inner and outer

  12. 9. Easy multi-choice The SA node is located near the juncture of the: A. Left atrium and left pulmonary veins B. Left atrium and right pulmonary veins C. Right atrium and superior vena cava D. Right atrium and inferior vena cava

  13. 10. Multi-choice If cardiac impulses are completely blocked at the bundle of His, then the atricular beat will be: A. Normal B. Slow C. Fast D. ceased

  14. 11. Multi-choice If cardiac impulses are completely blocked at the bundle of His, then the ventricular beat will be: A. Normal B. Slow C. Fast D. ceased

  15. 12. Multi-choice Which of the following would be expected to result in a decrease in ventricular contractility? A. hypercalcemia B. hypocalcemia C. hypokalemia D. hypernatremia

  16. 14. Nasty During an acute MI, extracellular potassium rises rapidly to 10-20mM. This will produce: • A. Decreased Na+ channel inactivation • B. Decreased threshold • C. Membrane hyperpolarization • D. Slowing of conduction The decreased K+ concentration gradient will increase the resting potential. This mean some Na channels will stay inactivated, reducing the available Na current. This will slow or block conduction.

  17. 15. Nasty In a patient with atrialtachyarrhythima, giving a drug that increases the effective refractory period in the AV node would be expected to: A. Abolish the arrhythmia B. Increase the PR interval (the time to conduct an impulse through the AV node) C. Slow the ventricular rate D. Induce a third degree AV block

  18. 16. Nasty A rise in intracellular concentration of which ion can indirectly result in an increase in ventricular contractility? A. Cl- B. K+ D. Na+ C. HCO3- Reducing the Na+ gradient makes the Na/Ca pump less effective, so less calcium is pumped out of the cell. The excess calcium is sucked into the sarcoplasmic reticulum, which then releases extra calcium on subsequent impulses, for more contractility.

  19. 17. Nasty The following condition can result in an increase in ectopic automaticity, resulting in an increased incidence of ventricular arrhythmias: A. hypercalcemia B. hyperkalemia C. hypokalemia D. hypermagnesemia E. hyponatremia Don’t understand why. Something to do with the K1 current?

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