Physio: Cardiac Electrophysiology

Front 1

Name the five areas where cells in the heart exhibit normal automaticity.

Back 1

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

Front 2

Which of the following is NOT a latent pacemaker?

A. AVN
B. Bundle Branches
C. Bundle of His
D. Purkinje fibers
E. SAN

Back 2

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

Front 3

What is overdrive suppression and ectopic pacemakers with regards to heart impulse formation?

Back 3

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

Front 4

The rate of firing of pacemakers is dependent on three factors that control:

Back 4

1. Max diastolic potential
2. Threshold potential
3. Rate of diastolic (phase 4) depolarization

Front 5

True or False:
Changes in heart AP duration significantly alter automaticity.

Back 5

FALSE. Because APD is much shorter than phase 3 (diastole), changes in APD DO NOT significantly alter automaticity. p. 333

Front 6

True or False:

Threshold potential is the voltage at which Na+ (or Ca 2+ in SAN or AVN) channels suddenly switch on.

Back 6

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

Front 7

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

Back 7

A. Absolute Refractory Period

p.334

Front 8

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

Back 8

small portion were the
B. Effective Refractory Period and C. Relative Refractory Period overlap


p.334

Front 9

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

Back 9

C. Relative Refractory Period

p.334

Front 10

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

Back 10

D. Supranormal Period

most prominent in Purkinje fibers

p.334

Front 11

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

Back 11

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

Front 12

Conduction velocity [ is / is not ] related to action potential duration.

Back 12

NOT. Conduction velocity reflects the time it takes for excitation to spread. APD reflects the time depolarization to threshold potential.

Front 13

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

Back 13

D. voltage-dependence inactivation

p.335

Front 14

Regarding impulse conduction in the heart, smaller inward currents will depolarize distant membrane more [ quickly / slowly ] and thereby [ speed up / slow ] conduction velocity.

Back 14

slowly, slow

p.335

Front 15

Action potentials are much longer in duration in cardiac muscle (up to _____ msec) than in nerve or skeletal muscle (__ msec).

Back 15

Cardiac m. = up to 400 msec
nerve or skeletal = ~ 5 msec

p.322

Front 16

The pacemaker of the heart is the _______.

Back 16

SAN p.323

Front 17

What do the following refer to affecting?
A. Chronotropic
B. Dromotropic
C. Inotropic

Back 17

A. Chronotropic = timing of heart beats
B. dromotropic = affects conduction speed
C. Inotropic = forces of heart m. contraction

Front 18

Increase of sympathetic activity in the SAN yields:

A. + chronotropic affects
B. + dromotropic affects
C. + inotropic affect

Back 18

A. + chronotropic affect

p.323

Front 19

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

Back 19

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

Front 20

What are the three requirements for a normal sinus rhythm of the heart?

Back 20

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

Front 21

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

Back 21

C. exhibit decreasing Ek as [K] outside decreases

p.325

Front 22

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

Back 22

system:
A. depolarizes at very low potassium levels

p.325

Front 23

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

Back 23

B. insensitive to K+ changes

p. 325

Front 24

Action potential duration is proportional to...

A. HR
B. 1/HR
C. Conduction Velocity
D. 1/ Conduction Velocity

Back 24

B. 1/HR
p. 325

Front 25

In the heart, Em is about ____ mV except in SAN and AVN where Em is ___ mV.

Back 25

-85 mV , then -60 mV

p. 326

Front 26

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.

Back 26

150- to 400 msec.
AVN ~ SAN ~ 150 msec.
Atria ~ 200 msec
Vent ~ 300 msec
PKJ ~ 400 msec

p. 325

Front 27

Upstroke is rapid except in which two areas of the heart?

Back 27

AVN and SAN

p. 325

Front 28

Which phases run together in SAN AND AVN and which phase is altogether absent?

Back 28

run together = phases 2 and 3
absent = phase 1

Front 29

The equilibrium potential, current inward during the action potential, and effect on Em during AP depolarization of Na+ is...

Back 29

+ 60 mV

p. 328

Front 30

The equilibrium potential, current during AP (inward/ outward) and effect on Em during AP (depolarizing, repolarizing, hyperpolarizing) of K+ is...

Back 30

-100 mV, outward, repolarizing and hyperpolarizing for gK and gK1 but for gTO, just repolarizing.

p. 328

Front 31

Know the ionic basis for phases of ventricular AP!

Back 31

do your white flashcards!

p.328

Front 32

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

Back 32

E. I Na

unless you are in the AVN or SAN, then the answer is B. I Ca

Front 33

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

Back 33

B. I Ca

Front 34

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

Back 34

B. I Ca

Front 35

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

Back 35

B. I Ca

Front 36

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

Back 36

B. I Ca

Front 37

L-type Ca2+ channels are modulated by agonist(s) ___________ and by antagonist(s) ____________.

Back 37

L-type Ca2+ channels are modulated by AGONIST NOREPHINEPHRINE and by ANTAGONISTS VERAPAMIL& ACETYLCHOLINE. p.331

Front 38

What type of Ca 2+ channels are more important in SAN than in other parts of the heart?

Back 38

T-type is more important in SAN but all other portions of the heart is predmoinantely L-type important.

Front 39

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, ]

Back 39

I K1

Front 40

The strong decrease in the conductance of ____ upon depolarization permits development of the plateau.

Back 40

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

Front 41

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, ]

Back 41

I K

Note: there are several types of I K in the heart. I Kr, I Ks, I Kur

Front 42

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, ]

Back 42

I to

Front 43

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 ].

Back 43

phase 2, slow turn on of I K and slow turn off of I Ca.

Front 44

Action potential duration decreases as HR [ decreases / increases ].

Back 44

APD decreases as HR increases

Front 45

What are the two reasons there is a plateau in heart AP but none in nerve?

Back 45

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.