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45 Cards in this Set
- Front
- Back
Name the five areas where cells in the heart exhibit normal automaticity.
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1. SAN
2. AVN 3. Bundle of His 4. Bundle Branches 5. Purkinje fibers the pacemaker with the fastest rate will control HR. Normally it occurs in this heirarchy. p.332 |
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Which of the following is NOT a latent pacemaker?
A. AVN B. Bundle Branches C. Bundle of His D. Purkinje fibers E. SAN |
E. SAN
latent pacemakers are cells that DO NOT normally exhibit normal automaticity. The others listed can take over but only if SAN is not working properly. p. 332 |
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What is overdrive suppression and ectopic pacemakers with regards to heart impulse formation?
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Latent pacemakers (cells that do not normally exhibit normal automaticity thought they have the capacity to do so) are also called ectopic pacemakers. Their suppression is called overdrive suppression. p.332
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The rate of firing of pacemakers is dependent on three factors that control:
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1. Max diastolic potential
2. Threshold potential 3. Rate of diastolic (phase 4) depolarization |
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True or False:
Changes in heart AP duration significantly alter automaticity. |
FALSE. Because APD is much shorter than phase 3 (diastole), changes in APD DO NOT significantly alter automaticity. p. 333
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True or False:
Threshold potential is the voltage at which Na+ (or Ca 2+ in SAN or AVN) channels suddenly switch on. |
FALSE. Rather, Na+ (and Ca2+) channnels begin to open at voltages far negative to the threshold potential. The fraction of resting channels that open increases gradually as the membrane is depolarized. p.333
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Regarding excitability changes during the heart AP, when is stimulation not possible?
A. Absolute Refractory Period B. Effective Refractory Period C. Relative Refractory Period D. Supranormal Period |
A. Absolute Refractory Period
p.334 |
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Regarding excitability changes during the heart AP, between which periods can an AP be elicited but not conducted (generates a local response but fails to conduct)?
A. Absolute Refractory Period B. Effective Refractory Period C. Relative Refractory Period D. Supranormal Period |
small portion were the
B. Effective Refractory Period and C. Relative Refractory Period overlap p.334 |
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Regarding excitability changes during the heart AP, when can an AP be elicited but with a larger current than at rest?
A. Absolute Refractory Period B. Effective Refractory Period C. Relative Refractory Period D. Supranormal Period |
C. Relative Refractory Period
p.334 |
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Regarding excitability changes during the heart AP, when can a current required for excitation equals less than required at rest?
A. Absolute Refractory Period B. Effective Refractory Period C. Relative Refractory Period D. Supranormal Period |
D. Supranormal Period
most prominent in Purkinje fibers p.334 |
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Recovery of .... is essential to recovery of excitability.
A. ability to generate an outward current B. ability to generate an inward current C. ability to control the threshold potential |
B. ability to generate an inward current
Recovery of the Na_ channel (or Ca2+ channel in the SAN or AVN) from the Inactivated (I) to Closed but available (C) state requires repolarization. p.334 p.334 |
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Conduction velocity [ is / is not ] related to action potential duration.
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NOT. Conduction velocity reflects the time it takes for excitation to spread. APD reflects the time depolarization to threshold potential.
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Which of the following is not a determinant of conduction velocity regarding heart impulse conduction?
A. amplitude of inward current B. excitability C. passive properties like membrane resistance and capacitance D. voltage-dependence inactivation |
D. voltage-dependence inactivation
p.335 |
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Regarding impulse conduction in the heart, smaller inward currents will depolarize distant membrane more [ quickly / slowly ] and thereby [ speed up / slow ] conduction velocity.
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slowly, slow
p.335 |
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Action potentials are much longer in duration in cardiac muscle (up to _____ msec) than in nerve or skeletal muscle (__ msec).
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Cardiac m. = up to 400 msec
nerve or skeletal = ~ 5 msec p.322 |
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The pacemaker of the heart is the _______.
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SAN p.323
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What do the following refer to affecting?
A. Chronotropic B. Dromotropic C. Inotropic |
A. Chronotropic = timing of heart beats
B. dromotropic = affects conduction speed C. Inotropic = forces of heart m. contraction |
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Increase of sympathetic activity in the SAN yields:
A. + chronotropic affects B. + dromotropic affects C. + inotropic affect |
A. + chronotropic affect
p.323 |
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What are the conduction velocities in the following areas:
A. atrial internodal tracts (SAN -> AVN) B. AV node C. His-Purkinje system D. ventricular muscle |
A. atrial internodal tract = 1 m/sec
B. AVN = 0.01 - 0.05 m/ sec C. His-Purk = 2-4 m/sec D. ventricular m. = 1 m/sec |
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What are the three requirements for a normal sinus rhythm of the heart?
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1. Impulse initiated at SAN
2. rate 60-100 bpm and regular 3. excitation must occur in a normal sequence with appropriate timing of excitation of various portions of the heart p.234 |
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Serum K+ affect resting membrane potentials (Em). The atria and ventricles:
A. depolarize at very low potassium levels B. are insensitive to K+ changes C. exhibit decreasing Ek as [K] outside decreases |
C. exhibit decreasing Ek as [K] outside decreases
p.325 |
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Serum K+ affect resting membrane potentials (Em). The His-Purkinje system:
A. depolarizes at very low potassium levels B. is insensitive to K+ changes C. exhibits decreasing Ek as [K] outside decreases |
system:
A. depolarizes at very low potassium levels p.325 |
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Serum K+ affect resting membrane potentials (Em). The SAN and AVN are:
A. depolarized at very low potassium levels B. insensitive to K+ changes C. prone to exhibit decreasing Ek as [K] outside decreases |
B. insensitive to K+ changes
p. 325 |
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Action potential duration is proportional to...
A. HR B. 1/HR C. Conduction Velocity D. 1/ Conduction Velocity |
B. 1/HR
p. 325 |
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In the heart, Em is about ____ mV except in SAN and AVN where Em is ___ mV.
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-85 mV , then -60 mV
p. 326 |
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An action potential in the heart can last anywhere from ___ to ___ msec. Order from least to greatest the various parts: Atria, AVN, PKJ, SAN, Vent.
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150- to 400 msec.
AVN ~ SAN ~ 150 msec. Atria ~ 200 msec Vent ~ 300 msec PKJ ~ 400 msec p. 325 |
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Upstroke is rapid except in which two areas of the heart?
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AVN and SAN
p. 325 |
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Which phases run together in SAN AND AVN and which phase is altogether absent?
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run together = phases 2 and 3
absent = phase 1 |
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The equilibrium potential, current inward during the action potential, and effect on Em during AP depolarization of Na+ is...
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+ 60 mV
p. 328 |
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The equilibrium potential, current during AP (inward/ outward) and effect on Em during AP (depolarizing, repolarizing, hyperpolarizing) of K+ is...
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-100 mV, outward, repolarizing and hyperpolarizing for gK and gK1 but for gTO, just repolarizing.
p. 328 |
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Know the ionic basis for phases of ventricular AP!
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do your white flashcards!
p.328 |
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This current is responsible for action potential upstroke.
A. I Cl B. I Ca C. I K D. I K1 E. I Na F. I to |
E. I Na
unless you are in the AVN or SAN, then the answer is B. I Ca |
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This current is responsible for inward current during plateau.
A. I Cl B. I Ca C. I K D. I K1 E. I Na F. I to |
B. I Ca
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This current turns on early in phase 2 and slowly turns off in phase 2.
A. I Cl B. I Ca C. I K D. I K1 E. I Na F. I to |
B. I Ca
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Inactivation of this current helps set action potential duration.
A. I Cl B. I Ca C. I K D. I K1 E. I Na F. I to |
B. I Ca
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This current reflects the activity of 2 disctinct channel types: T (transient) and L (longer lasting).
A. I Cl B. I Ca C. I K D. I K1 E. I Na F. I to |
B. I Ca
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L-type Ca2+ channels are modulated by agonist(s) ___________ and by antagonist(s) ____________.
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L-type Ca2+ channels are modulated by AGONIST NOREPHINEPHRINE and by ANTAGONISTS VERAPAMIL& ACETYLCHOLINE. p.331
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What type of Ca 2+ channels are more important in SAN than in other parts of the heart?
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T-type is more important in SAN but all other portions of the heart is predmoinantely L-type important.
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Which current is responsible for resting potential? (Hint: Think which conductance is high during phase 4?)
[ I Cl, I Ca, I K, I K1, I Na, I to, ] |
I K1
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The strong decrease in the conductance of ____ upon depolarization permits development of the plateau.
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gK1. decreased gK1 limits the increase of I k1 that otherwise would result from increased K+ driving force during plateau and prevents rapidly repolarization of myocytes.
p.331 |
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Which current slowly turns on during phase 2 and its slow increase helps set action potential duration.
[ I Cl, I Ca, I K, I K1, I Na, I to, ] |
I K
Note: there are several types of I K in the heart. I Kr, I Ks, I Kur |
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This current contributes to phase 1 repolarization, especially in epicardial ventricular muscle and in Purkinge fibers.
[ I Cl, I Ca, I K, I K1, I Na, I to, ] |
I to
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The action potential duration, primarily the length of phase ___ , is set by the slow turn on (activation) of [ which current ] and the slow turn off (inactivation) of [ which current ].
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phase 2, slow turn on of I K and slow turn off of I Ca.
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Action potential duration decreases as HR [ decreases / increases ].
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APD decreases as HR increases
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What are the two reasons there is a plateau in heart AP but none in nerve?
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1. I Ca is absent or insignificant in nerve whereas in heart, it provides the inward current to maintain the depolarization
2. decrease in gK1 on depolarization in heart makes it easier to maintain plateau. In nerve, gK1 does NOT decrease thus repolarization occurs within msec. |