front 1 A normal heartbeat is initiated in the: A. SA node | back 1 A. SA node |
front 2 After originating in the sinus node, the impulse next normally travels to the: A. bundle branches | back 2 C. AV node |
front 3 At the AV node, impulses are normally: A. accelerated | back 3 B. delayed |
front 4 The AV bundle normally conducts impulses from the: A. ventricles to atria | back 4 D. atria into ventricles |
front 5 The right and left bundle branches ultimately distribute impulses to: A. both atria | back 5 B. all ventricular regions |
front 6 The sinus node is located in the: A. superior posterolateral right atrium | back 6 A. superior posterolateral right atrium |
front 7 Relative to the superior vena cava opening, the sinus node lies: A. medial and above | back 7 D. below and lateral |
front 8 Sinus nodal fibers connect directly to atrial muscle fibers so that: A. ventricular filling begins sooner | back 8 C. atrial depolarization spreads immediately |
front 9 Some cardiac fibers can spontaneously depolarize, producing rhythmic discharge. This property is called: A. self-excitation | back 9 A. self-excitation |
front 10 The resting membrane potential of sinus nodal fibers is normally closest to: A. -90 to -95 mV | back 10 B. -55 to -60 mV |
front 11 Sinus nodal cells are less negative than ventricular cells mainly because they are naturally leaky to: A. potassium and chloride | back 11 D. sodium and calcium |
front 12 Which list correctly names the three main cardiac ion channels? A. chloride, sodium, magnesium | back 12 C. fast sodium, L-type calcium, potassium |
front 13 Because the sinus node membrane potential is less negative, which channels remain closed during nodal action potential generation? A. potassium channels | back 13 B. fast sodium channels |
front 14 The sinus nodal action potential upstroke is slower than ventricular muscle because nodal cells rely mainly on: A. slow sodium-calcium channels | back 14 A. slow sodium-calcium channels |
front 15 Between heartbeats, the slow rise in sinus nodal resting membrane potential is caused mainly by: A. potassium leaving the cell | back 15 C. sodium influx |
front 16 When sinus nodal membrane potential reaches threshold, about _____, L-type calcium channels open. A. -90 mV | back 16 D. -40 mV |
front 17 The self-excitation of sinus nodal fibers is due primarily to their A. inherent leakiness | back 17 A. inherent leakiness |
front 18 To avoid remaining continuously depolarized, sinus nodal fibers do which of the following? A. open fast sodium channels, lose potassium | back 18 B. inactivate calcium channels, lose potassium |
front 19 Which additional event helps terminate the sinus nodal action potential and prevent persistent depolarization? A. sodium retention in cell | back 19 D. potassium diffusion outward |
front 20 Excess negativity developing inside the fiber after repolarization is called: A. depolarization | back 20 C. hyperpolarization |
front 21 Which sequence best describes the sinus node action-potential process? A. Self-excitation, recovery, hyperpolarization, threshold drift,
re-excitation | back 21 A. Self-excitation, recovery, hyperpolarization, threshold drift, re-excitation |
front 22 Rapid activation of the left atrium after sinus node discharge is aided most directly by the: A. middle internodal tract | back 22 D. anterior interatrial band |
front 23 Which tracts conduct impulses from the SA node to the AV node? A. anterior, lateral, septal pathways | back 23 B. anterior, middle, posterior internodal pathways |
front 24 Which structure primarily delays transmission before impulses enter the ventricles? A. SA node | back 24 C. AV node |
front 25 During EP mapping, a conduction structure is identified in the posterior wall of the right atrium behind the tricuspid valve. This is the: A. AV node | back 25 A. AV node |
front 26 The total delay in the AV node plus AV bundle is closest to: A. 0.03 seconds | back 26 C. 0.13 seconds |
front 27 The conduction delay between the sinus node and AV node is approximately: A. 0.13 seconds | back 27 D. 0.03 seconds |
front 28 The total delay before the excitatory signal reaches contracting ventricular muscle is about: A. 0.13 seconds | back 28 B. 0.16 seconds |
front 29 Slow conduction through nodal tissue occurs mainly because of diminished numbers of: A. gap junctions | back 29 A. gap junctions |
front 30 Which fibers continue from the AV node through the AV bundle into the ventricles? A. atrial conducting fibers | back 30 D. special Purkinje fibers |
front 31 Purkinje fibers are best described as: A. small fibers, rapid contraction | back 31 C. large fibers, fast conduction |
front 32 The conduction velocity in Purkinje fibers is closest to: A. 0.3 to 0.5 m/sec | back 32 B. 1.5 to 4.0 m/sec |
front 33 Rapid Purkinje transmission is attributed mainly to the very high permeability of: A. gap junctions at discs | back 33 A. gap junctions at discs |
front 34 Purkinje fibers contract very little during impulse transmission because they contain few: A. intercalated discs | back 34 D. myofibrils |
front 35 Which statement is a special characteristic of the AV bundle? A. It conducts only retrograde impulses | back 35 C. Impulses normally cannot travel backward |
front 36 The only site where atrial muscle is not separated from ventricular muscle is the: A. AV node | back 36 B. AV bundle |
front 37 The continuous fibrous barrier between atrial and ventricular muscle normally acts as an: A. insulator | back 37 A. insulator |
front 38 The left and right bundle branches travel primarily: A. upward toward the base | back 38 C. downward toward the apex |
front 39 The terminal Purkinje fibers penetrate into the ventricular muscle mass approximately: A. halfway through myocardium | back 39 D. one-third of the way |
front 40 A lesion affecting the fibrous insulating barrier but sparing the AV bundle would most likely alter which normal property of the heart? A. Purkinje automaticity | back 40 B. electrical separation of atria and ventricles |
front 41 The gross arrangement of cardiac muscle around the heart is best described as a: A. double spiral | back 41 A. double spiral |
front 42 Between the spiraling layers of cardiac muscle lie: A. Purkinje sheets | back 42 D. fibrous septa |
front 43 The total time for impulse transmission from the bundle branches to the last ventricular muscle fibers is closest to: A. 0.16 seconds | back 43 C. 0.06 seconds |
front 44 If isolated from faster pacemakers, AV nodal fibers typically discharge at an intrinsic rate of: A. 15-40/min | back 44 B. 40-60/min |
front 45 Purkinje fibers, when acting as an intrinsic pacemaker, usually discharge at: A. 15-40/min | back 45 A. 15-40/min |
front 46 The normal discharge rate of the sinus node is about: A. 15-40/min | back 46 C. 70-80/min |
front 47 The SA node normally controls cardiac rhythmicity primarily because it has the: A. longest refractory period | back 47 B. highest discharge rate |
front 48 A pacemaker located anywhere other than the sinus node is called an: A. escape focus | back 48 C. ectopic pacemaker |
front 49 Blockage of cardiac impulse transmission can cause a: A. shift of pacemaker | back 49 A. shift of pacemaker |
front 50 AV block refers to failure of the cardiac impulse to pass from the: A. ventricles to atria | back 50 C. atria to ventricles |
front 51 In complete AV block, which chambers continue to beat at their own normal rhythm? A. ventricles | back 51 B. atria |
front 52 In AV block, the structure that usually becomes the pacemaker for the ventricles is the: A. SA node | back 52 D. Purkinje system |
front 53 A patient with complete AV block briefly has no effective ventricular rhythm before a slow escape rhythm appears. This delay occurs because the Purkinje fibers are initially: A. overstimulated | back 53 C. in a suppressed state |
front 54 In Stokes-Adams syndrome, the Purkinje system may fail to begin firing for approximately: A. 1-2 seconds | back 54 B. 5-20 seconds |
front 55 A patient with sudden complete AV block loses consciousness after a few seconds because cerebral blood flow ceases. Syncope usually occurs after about: A. 1-2 seconds | back 55 D. 4-5 seconds |
front 56 The delayed pickup of ventricular beating after AV block is called: A. ventricular fibrillation | back 56 C. Stokes-Adams syndrome |
front 57 Parasympathetic fibers to the heart are distributed mainly to the: A. SA and AV nodes | back 57 A. SA and AV nodes |
front 58 Sympathetic fibers are distributed to: A. only the atria | back 58 B. all parts of heart |
front 59 The main neurotransmitter mediating parasympathetic control of the heart is: A. epinephrine | back 59 C. acetylcholine |
front 60 Parasympathetic stimulation has two major cardiac effects: decreased SA nodal rate and decreased excitability of the: A. Purkinje fibers | back 60 D. AV junctional fibers |
front 61 Ventricular escape refers to the ability of the Purkinje fibers to: A. block atrial conduction | back 61 B. pace ventricles independently |
front 62 Acetylcholine released from vagal nerves greatly increases membrane permeability to: A. sodium ions | back 62 D. potassium ions |
front 63 Sympathetic stimulation of the heart causes increased SA discharge, increased conduction, and increased: A. force of contraction | back 63 A. force of contraction |
front 64 Stimulation of sympathetic cardiac nerves releases: A. epinephrine | back 64 C. norepinephrine |
front 65 Norepinephrine exerts its main cardiac effects through: A. alpha-1 receptors | back 65 D. beta-1 receptors |
front 66 Sympathetic stimulation increases membrane permeability primarily to: A. potassium and chloride | back 66 B. sodium and calcium |