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110 Cards in this Set
- Front
- Back
Which has a sharper peak in membrane potential, a nerve cell or a cardiac myocyte?
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Nerve cell
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What is the Keq of Na+?
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+72 mV
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What is the Keq of K+?
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-88 mV
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What is the Keq of Ca2+?
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+123 mV
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What determines membrane potential (resting and action potential)?
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Ionic diffusion
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The electrical events in the heart initiate what?
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Cardiac contraction
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Rhythmical electrical activity generates what?
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Rhythmical contraction of the heart
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What are the two types of action potential in the heart?
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Cardiac myocyte and pacemaker AP
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Which type of action potential is associated with conducting and contracting AP via bundle of His, purkinje fibers, atrial and ventricular myocytes?
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Cardiac myocyte AP
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Which action potential in the heart is a fast response?
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Cardiac myocyte AP
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Which type of action potential in the heart is auto-rhythmic and generates the same action potential periodically over long periods of time (SA and AV nodes).
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Pacemaker AP
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Which type of action potential in the heart is a slow response?
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Pacemaker AP
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Name the phases of action potential from a ventricular cardiac myocyte. (Phases 0-4)
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Phase 0: Rapid depolarization
Phase 1: Early partial repolarization Phase 2: Plateau phase Phase 3: Final repolarization Phase 4: Resting potential |
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What is occurring in the cardiac myocyte during rapid depolarization?
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The fast Na+ channel is open and Na+ ions are rushing into the cell (chemically and electrostatically, moreso chemically).
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What is occurring in the cardiac myocyte during early partial repolarization?
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The K+ channel is open, allowing K+ ions to leave the cell (chemically and electrostatically).
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What is occurring in the cardiac myocyte during the plateau phase?
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The Ca2+ and K+ channels are both open, allowing Ca2+ to enter the cell chemically (moreso) and leave the cell electrostatically, and K+ to leave the cell (chemically and electrostatically, moreso chemically).
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What is occurring in the cardiac myocyte during final repolarization?
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The K+ channels are open, allowing K+ ions to leave the cell chemically (moreso) and enter the cell electrostatically.
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What is occurring in the cardiac myocyte during the resting potential?
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The K+ channels are open, allowing K+ ions to enter the cell chemically and leave the cell electrostatically.
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Which phase of the ventricular cardiac myocyte involves a rapid Na+ influx through the voltage-gated Na+ channels (fast Na+ channels)?
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Phase 0: Rapid depolarization
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Which phase of the ventricular cardiac myocyte involves the efflux of K+, the transient outward K+ current (I to)?
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Phase 1: Early partial repolarization
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Which phase of the ventricular cardiac myocyte involves an increased Ca++ conductance?
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Phase 2: Plateau phase
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Which phase of the ventricular cardiac myocyte involves the efflux of K+ exceeding the influx of Ca++?
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Phase 3: Final Repolarization
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Which phase of the ventricular cardiac myocyte is determined mainly by the K+ conductance?
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Phase 4: Resting potential
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Which type of channel is this?
Voltage-gated channels, phase 0 depolarization of non-pacemaker cardiac action potentials |
Fast Na+ channels
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Which type of channel is this?
Maintains resting membrane potential (phase 4), permits K outflow at highly negative potential in cardiac cells |
Inward rectifier: I(ir) or I(K1)
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Which type of channel is this?
Contributes to phase 1 by transiently permitting K outflow at positive membrane potential |
Transient outward: I(to)
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What type of channel is this?
Phase 3 repolarization of cardiac action potentials, permits K outflow |
Delayed rectifier: I(Kr)
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What type of channel is this?
KATP channels; inhibited by ATP; therefore, open when ATP decreases during hypoxia |
ATP-sensitive: I(K, ATP)
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What type of channel is this?
Activated by acetylcholine and adenosine; G-protein coupled, hyperpolarizes membrane during phase 4 and shortens phase 2 |
Acetylcholine-activated I(K, ACh) and adenosine-activated
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What type of channel is this?
Voltage-gated channels, slow inward, long-lasting current; phase 2 non-pacemaker cardiac action potentials |
L-type: I(Ca-L)
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During phase 0, 1, and part of 3 the cell is refractory to the initiation of any new action potentials. What is this called?
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Effective refractory period (ERP, absolute)
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Early in this phase, suprathreshold stimuli are required to elicit an AP. All Na+ channels are still not completely reactivated. What is this called?
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Relative refractory period (RRP)
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The ERP acts as a protective mechanism in the heart by preventing a)____________.
If these were to occur, what would happen to the heart? |
a) multiple APs or tetany
b) The heart would be unable to adequately fill with blood and eject blood. |
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Why doesn't the cell produce new, propagated AP during ERP (effective refractory period)?
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Because the fast Na+ channels are not fully reactivated and therefore cannot be reopened
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What limits the frequency of action potentials, and therefore contractions?
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The length of the refractory period
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Pacemaker cells have unstable resting potentials called what?
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Pacemaker potentials
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What cells use Ca2+ influx for rising phase (phase 0) of the action potential?
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Pacemaker cells
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Which has a higher resting potential: pacemaker cells or non-pacemaker cells?
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Pacemaker cells (at -60 mV compared to -90 mV)
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What are the 3 phases of action potential (ionic currents)?
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Phase 0: Upstroke
Phase 3: Repolarization Phase 4: Slow (spontaneous) depolarization |
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Slow depolarization (phase 4) of pacemakers occurs due to the opening of what?
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Special type of Na+ channel called the funny current (If)
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When does the special type of Na+ channel called the funny current (If) open and close?
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opens when the cell hyperpolarizes (- 60 mV) and closes when the membrane depolarizes (-20 mV)
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In the later part of phase 4 (slow depolarization in pacemakers) there is a small (decrease/increase) in Ca2+ through ____________ channels. These channels open only briefly at ~ -50mV. As potential becomes more positive, _____________ channels begin to open until threshold is reached and many voltage gated Ca2+ channels open.
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Increase, T-type Ca2+, L-type Ca2+
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What phase of pacemakers is this?
Opening of voltage gated L- type Ca2+ channels at -40 mV, accompanied by low K+ conductance. Voltage gated L- type Ca2+ channels are slower than the Na+ channel in non-pacemaker cells (NO fast Na+ channels in SA and AV nodes). This depolarizes membrane towards +132 mV. |
Phase 0 – upstroke
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What phase of pacemakers is this?
Voltage gated Ca2+ channels become inactivated and voltage gated delayed rectifier K+ channels open. Since K+ dominates, membrane potential moves toward – 94 mV. |
Phase 3 - repolarization
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Name the K+ channel.
Activated by Ach and adenosine; G-protein coupled, hyperpolarizes membrane during phase 4 slowing pacemaker potential. |
G-protein coupled receptors: Ach-activated (IK, ACh) and adenosine-activated
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Name the Na+ channel.
"Funny" pacemaker current (If) in cardiac nodal tissue. |
Slow Na+ - I(f)
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Name the Ca2+ channel.
Transient current that contributes to phase 4 pacemaker currents in SA and AV nodal cells Many of the antiarrhythmic drugs that are used to treat cardiac arrhythmias have their action on Na+ ,Ca++, and K+ channels |
T-Type - I(Ca-T)
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What ion channels are involved in Purkinje and ventricular myocyte membrane potential?
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Na+:
Fast Na+ K+: Inward rectifier Transient outward Delayed rectifier ATP-sensitive Acetylcholine-activated and adenosine-activated Ca2+: L-type |
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What ion channels are involved in pacemaker potential?
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Na+:
Slow Na+ K+: Delayed rectifier ATP-sensitive G-protein coupled receptors: Ach-activated (IK, ACh) and adenosine-activated Ca2+: L-type T-type |
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T/F
In pacemaker cells, the relative refractory period (RRP) extends beyond phase 3. |
True!
(Post-repolarization refractoriness) |
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In pacemaker cells, the recovery of full excitability is much (slower/faster) than in fast-response AP.
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Slower
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In pacemaker cells, impulses that arrive early in the RRP are conducted (slower/faster) than those that arrive late in the RRP
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Slower
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What do the lengthy refractory periods in pacemaker cells lead to?
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Conduction blocks
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T/F
Even when slow-response APs recur at a slow repetition rate, the cells may be able to conduct only a fraction of those impulses (only alternate impulses) |
True!
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What heart rate is tachycardia?
When can this heart rate be considered normal? |
HR > 100 bmp
Can be normal during exercise. |
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What heart rate is bradycardia?
When can this heart rate be considered normal? |
HR < 60 bpm
Can be normal especially in endurance athletes |
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What nerve has projections on the SA and AV node (predominantly)?
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Vagus nerve
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The sympathetic nerve fibers innervate both ____________(predominanlty) and to some (very little) extent _______________.
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Cardiac muscle, pacemaker cells
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What is responsible for the interactions between the sympathetic and parasympatheic systems?
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Interneuronal mechanisms
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Sympathetic (NE) neurons (inhibit/stimulate) the heart, while parasympathetic (Ach) neurons (inhibit/stimulate) the heart.
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Stimulate, inhibit
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Which neurons cause positive chronotropic (↑HR) , dromotropic (↑ conduction velocity of electrical impulses) and ionotropic (↑ contractile forces) effects?
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Sympathetic (NE) neurons
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Which neurons cause negative chronotropic, dromotropic, and ionotropic effects?
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Parasympathetic (Ach) neurons
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Doing what to the pacemaker cells in the SA and AV nodes reduces heart rate?
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Decreasing firing frequency
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How can firing frequency be reduced?
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By increasing the length of the effective (absolute) refractory period (↑ERP):
Increasing the duration of AP Increasing the maximal negative potential (hyperpolarization during the phase 4) |
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What decreases I(f) current in reducing steepness of phase 4 (↑ERP), sympathetic or parasympathetic?
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Parasympathetic (Ach)
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What reduces Ca++ current (ICa-T) channelsm reducing steepness of phase 4 and moving threshold more positive (↑ERP), sympathetic or parasympathetic innervation?
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Parasympathetic
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What opens G-protein coupled K+ channels, increasing K+ conductance and maxing diastolic potential more negative (hyperpolarizing membrane), sympathetic or parasympathetic stimulation?
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Parasympathetic (Ach)
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What acts through beta-1 adrenergic receptors to increase heart rate (chronotropy) (↓ERP)?
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Catecholamines
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Catecholamines __________ I(f) current in SA node, therefore increasing steepness of _________.
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Increase, phase 4
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Catecholamines __________ Ca2+ current in all myocardial cells increasing steepness of _________ and moving threshold more __________.
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Increase, phase 4, negative
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Ca2+ channel blockers:
a) __________ the slope of phase 4, thereby decreasing the rate of ______________. b) __________ the slope of phase 0, which slows the ____________ within the _____ node. c) __________ the threshold potential level. |
a) reduce, spontaneous depolarization
b) decrease, conduction velocity, AV c) increase |
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Blockers of the delayed rectifier K+ channel increase the length of what?
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Phase 3 repolarization
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Activation of G-protein-coupled K+-channels increases what?
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The maximal negative potential
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How does decreasing the Na+ funny current I(f) affect the slope of phase 4?
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Decreases the slope of phase 4
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What are the mechanisms that decrease the firing frequency of pacemaker cells?
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Ca2+ channel blockers
Blockers of the delayed rectifier K+ channel Activation of G-protein-coupled K+-channels Decreasing Na+ funny current I(f) |
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What are 4 common causes of abnormal electrical activity in the heart?
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Inadequate myocardial blood flow (myocardial hypoxia)
Changes in ion concentrations in the ECF ([K+]o, [Ca+ +]o, [Na+]o,) Changes in membrane ionic conductances (ion channels, exchangers) Changes in the ATPase (Na,K-ATPase, Ca-ATPase) |
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What are 2 common consequences of abnormal electrical activity in the conducting and contracting myocytes?
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Transformation of non-pacemaker into pacemaker cell action potential (ectopic beats)
Alteration of duration of the refractory period (abnormal myocardial contractility and rate of contraction) |
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Low O2 supply (atherosclerosis, stenosis, spasm) and increased O2 demands (increased myocardial contractility) can lead to what?
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Inadequate myocardial blood flow, causing myocardial hypoxia.
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Patients with what disease may develop myocardial hypoxia in response to exercise or at rest (in more severe cases)?
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Coronary artery disease
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A decrease in ATP synthesis (impairment of ATPases activity)
Local accumulation of tissue metabolites Impaired Na,K-ATPase activity([K+]o is elevated) These are consequences of what? |
Inadequate O2 supply
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When [K+]o is increased:
a) The resting Vm becomes (less/more) negative. b) The amplitude, duration of the AP and the steepness of the upstroke all ________. c) _______________ is diminished. |
a) Less
b) Diminish c) Conduction velocity |
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In response to hypoxia, the membrane a)__________ and closes b)__________ channels (at a membrane potential of about –50 mV all the fast Na + channels are c)__________).
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a) Depolarizes
b) Fast Na+ c) Inactivated |
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In regards to myocardial hypoxia: transformation of non-pacemaker into pacemaker cells AP...
Action potentials can be elicited: a) by the inward _____ current b) similar to those found in pacemaker cells located in the ___________. c) never spontaneously (T/F?) |
a) Ca++
b) SA or AV nodes c) false! sometimes spontaneously |
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In ischemic heart disease, what mechanism may serve as the electrophysiological mechanism behind certain types of ectopic beats and irregular heart rate?
(decreasing cardiac output) |
Transformation of nonpacemaker into pacemaker cells AP (from myocardial hypoxia)
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What toxin blocks the voltage-gated Na+ channels?
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Tetrodotoxin
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T/F
Many antiarrhythmic drugs increase the ERP (effective refractory period), thereby altering cellular excitability. |
True!
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Which channel blockers delay phase 3 repolarization and increase the action potential duration?
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K+ channel blockers
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Which channel blockers decrease slope of the phase 0, depress the peak of the AP, and increase the inactivation state of fast-Na channels (voltage-gated Na-channels)?
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Na+ channel blockers
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Name the failure of propagation in a cardiac fiber.
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Conduction block
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What is it called when a cardiac impulse reenters previously excited tissue when the impulse is conducted slowly around the loop and the impulse is blocked unidirectionally in some sections of the loop.
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Reentry
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What is the term for increased or depressed normal firing rate of pacemaker cells in the SA or/and AV nodes.
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Abnormal automaticity
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Abnormal automaticity can be caused by what?
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Abnormal autonomic regulation
Other factors (metabolic, pharmacological, mechanical): Hypo/hyper – kalemia , cardiac fiber stretch, β-adrenergic receptor activation, tissue injury Ectopic pacemaker activity: Increased automaticity of pacemakers outside of the SA |
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What type of afterdepolarization occurs at the end of phase 2 or about midway phase 3 (ionic mechanism is not clearly understood)?
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Early afterdepolarization (EAD)
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What type of afterdepolarization occurs at the end or just after full repolarization ( associated with elevated [Ca++]i)?
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Late afterdepolarization (LAD)
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What are 3 reasons for tachycardia?
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Increased automaticity: anything that increases rate of the pacemaker. Drugs, sympathetic stimulation
Spontaneous depolarizations: can occur during phase 3 or 4 of AP and referred to as triggered tachycardias. This can be caused by mutation in ion channels An ectopic pacemaker (ectopic focus): a single beat or series of beats that occurs outside the normal pacemaker region (premature systole). |
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What are 2 reasons for bradycardia?
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Depressed impulse formation: pacemaker problem in the SA node.
-Abnormal autonomic influences (due to excessive parasymapthetic tone) Impaired impulse conduction: A block in the conduction pathway slows the electrical signal -Tissue damage, change in anatomy -Drugs |
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An ECG measures electrical difference between two of what?
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Surface electrodes placed near the heart
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ECG is a measure of what two variables?
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Voltage and time
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In an ECG, what are bipolar leads?
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I,II, and III
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In an ECG, what are unipolar leads?
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Unipolar:
Limbs: LA, LL, RA Chest leads: V1-V6 |
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What does phase 0 (upstroke) of ventricular AP correspond to in the ECG?
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R wave
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What does phase 2 (plateau) of ventricular AP correspond to of the ECG?
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ST segment
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What does phase 3 (repolarization) of the ventricular AP corresponds to in the ECG?
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T wave (ventricular repolarization)
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What 5 structures CAN'T the ECG show electrical acitivity of?
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SA node, AV node, bundle branches, bundle of His, and Purkinje network
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What interval on an ECG does atrial depolarization and conduction through AV node occur?
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PR
(.12-.20 sec) |
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What interval on an ECG does ventricular depolarization
atrial repolarization occur? |
QRS
(.08-.10 sec) |
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What interval on an ECG does ventricular depolarization and ventricular repolarization occur?
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QT
(.40 - .43 sec) |
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What interval on an ECG does ventricular repolarization
(QT minus QRS) occur? |
ST
(.32 sec) |
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What do you use in the ECG for the heart rate?
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R-R interval (1 beat) during time interval
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What is the term for a subtle change in HR with respiratory cycle? Inspiration accelerates, expiration slows.
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Sinus arrhythmia
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