S2 Bsf Exam1: Electrical Activity Of Heart

Front 1

Which has a sharper peak in membrane potential, a nerve cell or a cardiac myocyte?

Back 1

Nerve cell

Front 2

What is the Keq of Na+?

Back 2

+72 mV

Front 3

What is the Keq of K+?

Back 3

-88 mV

Front 4

What is the Keq of Ca2+?

Back 4

+123 mV

Front 5

What determines membrane potential (resting and action potential)?

Back 5

Ionic diffusion

Front 6

The electrical events in the heart initiate what?

Back 6

Cardiac contraction

Front 7

Rhythmical electrical activity generates what?

Back 7

Rhythmical contraction of the heart

Front 8

What are the two types of action potential in the heart?

Back 8

Cardiac myocyte and pacemaker AP

Front 9

Which type of action potential is associated with conducting and contracting AP via bundle of His, purkinje fibers, atrial and ventricular myocytes?

Back 9

Cardiac myocyte AP

Front 10

Which action potential in the heart is a fast response?

Back 10

Cardiac myocyte AP

Front 11

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).

Back 11

Pacemaker AP

Front 12

Which type of action potential in the heart is a slow response?

Back 12

Pacemaker AP

Front 13

Name the phases of action potential from a ventricular cardiac myocyte. (Phases 0-4)

Back 13

Phase 0: Rapid depolarization
Phase 1: Early partial repolarization
Phase 2: Plateau phase
Phase 3: Final repolarization
Phase 4: Resting potential

Front 14

What is occurring in the cardiac myocyte during rapid depolarization?

Back 14

The fast Na+ channel is open and Na+ ions are rushing into the cell (chemically and electrostatically, moreso chemically).

Front 15

What is occurring in the cardiac myocyte during early partial repolarization?

Back 15

The K+ channel is open, allowing K+ ions to leave the cell (chemically and electrostatically).

Front 16

What is occurring in the cardiac myocyte during the plateau phase?

Back 16

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).

Front 17

What is occurring in the cardiac myocyte during final repolarization?

Back 17

The K+ channels are open, allowing K+ ions to leave the cell chemically (moreso) and enter the cell electrostatically.

Front 18

What is occurring in the cardiac myocyte during the resting potential?

Back 18

The K+ channels are open, allowing K+ ions to enter the cell chemically and leave the cell electrostatically.

Front 19

Which phase of the ventricular cardiac myocyte involves a rapid Na+ influx through the voltage-gated Na+ channels (fast Na+ channels)?

Back 19

Phase 0: Rapid depolarization

Front 20

Which phase of the ventricular cardiac myocyte involves the efflux of K+, the transient outward K+ current (I to)?

Back 20

Phase 1: Early partial repolarization

Front 21

Which phase of the ventricular cardiac myocyte involves an increased Ca++ conductance?

Back 21

Phase 2: Plateau phase

Front 22

Which phase of the ventricular cardiac myocyte involves the efflux of K+ exceeding the influx of Ca++?

Back 22

Phase 3: Final Repolarization

Front 23

Which phase of the ventricular cardiac myocyte is determined mainly by the K+ conductance?

Back 23

Phase 4: Resting potential

Front 24

Which type of channel is this?

Voltage-gated channels, phase 0 depolarization of non-pacemaker cardiac action potentials

Back 24

Fast Na+ channels

Front 25

Which type of channel is this?

Maintains resting membrane potential (phase 4), permits K outflow at highly negative potential in cardiac cells

Back 25

Inward rectifier: I(ir) or I(K1)

Front 26

Which type of channel is this?

Contributes to phase 1 by transiently permitting K outflow at positive membrane potential

Back 26

Transient outward: I(to)

Front 27

What type of channel is this?

Phase 3 repolarization of cardiac action potentials, permits K outflow

Back 27

Delayed rectifier: I(Kr)

Front 28

What type of channel is this?

KATP channels; inhibited by ATP; therefore, open when ATP decreases during hypoxia

Back 28

ATP-sensitive: I(K, ATP)

Front 29

What type of channel is this?

Activated by acetylcholine and adenosine; G-protein coupled, hyperpolarizes membrane during phase 4 and shortens phase 2

Back 29

Acetylcholine-activated I(K, ACh) and adenosine-activated

Front 30

What type of channel is this?

Voltage-gated channels, slow inward, long-lasting current; phase 2 non-pacemaker cardiac action potentials

Back 30

L-type: I(Ca-L)

Front 31

During phase 0, 1, and part of 3 the cell is refractory to the initiation of any new action potentials. What is this called?

Back 31

Effective refractory period (ERP, absolute)

Front 32

Early in this phase, suprathreshold stimuli are required to elicit an AP. All Na+ channels are still not completely reactivated. What is this called?

Back 32

Relative refractory period (RRP)

Front 33

The ERP acts as a protective mechanism in the heart by preventing a)____________.
If these were to occur, what would happen to the heart?

Back 33

a) multiple APs or tetany
b) The heart would be unable to adequately fill with blood and eject blood.

Front 34

Why doesn't the cell produce new, propagated AP during ERP (effective refractory period)?

Back 34

Because the fast Na+ channels are not fully reactivated and therefore cannot be reopened

Front 35

What limits the frequency of action potentials, and therefore contractions?

Back 35

The length of the refractory period

Front 36

Pacemaker cells have unstable resting potentials called what?

Back 36

Pacemaker potentials

Front 37

What cells use Ca2+ influx for rising phase (phase 0) of the action potential?

Back 37

Pacemaker cells

Front 38

Which has a higher resting potential: pacemaker cells or non-pacemaker cells?

Back 38

Pacemaker cells (at -60 mV compared to -90 mV)

Front 39

What are the 3 phases of action potential (ionic currents)?

Back 39

Phase 0:  Upstroke
Phase 3: Repolarization
Phase 4:   Slow (spontaneous) depolarization

Front 40

Slow depolarization (phase 4) of pacemakers occurs due to the opening of what?

Back 40

Special type of Na+ channel called the funny current (If)

Front 41

When does the special type of Na+ channel called the funny current (If) open and close?

Back 41

opens when the cell hyperpolarizes (- 60 mV) and closes when the membrane depolarizes (-20 mV)

Front 42

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.

Back 42

Increase, T-type Ca2+, L-type Ca2+

Front 43

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.

Back 43

Phase 0 – upstroke

Front 44

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.

Back 44

Phase 3 - repolarization

Front 45

Name the K+ channel.

Activated by Ach and adenosine; G-protein coupled, hyperpolarizes membrane during phase 4 slowing pacemaker potential.

Back 45

G-protein coupled receptors: Ach-activated (IK, ACh) and adenosine-activated

Front 46

Name the Na+ channel.

"Funny" pacemaker current (If) in cardiac nodal tissue.

Back 46

Slow Na+ - I(f)

Front 47

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

Back 47

T-Type - I(Ca-T)

Front 48

What ion channels are involved in Purkinje and ventricular myocyte membrane potential?

Back 48

Na+:
Fast Na+

K+:
Inward rectifier
Transient outward
Delayed rectifier
ATP-sensitive
Acetylcholine-activated and adenosine-activated

Ca2+:
L-type

Front 49

What ion channels are involved in pacemaker potential?

Back 49

Na+:
Slow Na+

K+:
Delayed rectifier
ATP-sensitive
G-protein coupled receptors: Ach-activated (IK, ACh) and adenosine-activated

Ca2+:
L-type
T-type

Front 50

T/F

In pacemaker cells, the relative refractory period (RRP) extends beyond phase 3.

Back 50

True!

(Post-repolarization refractoriness)

Front 51

In pacemaker cells, the recovery of full excitability is much (slower/faster) than in fast-response AP.

Back 51

Slower

Front 52

In pacemaker cells, impulses that arrive early in the RRP are conducted (slower/faster) than those that arrive late in the RRP

Back 52

Slower

Front 53

What do the lengthy refractory periods in pacemaker cells lead to?

Back 53

Conduction blocks

Front 54

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)

Back 54

True!

Front 55

What heart rate is tachycardia?

When can this heart rate be considered normal?

Back 55

HR > 100 bmp

Can be normal during exercise.

Front 56

What heart rate is bradycardia?

When can this heart rate be considered normal?

Back 56

HR < 60 bpm

Can be normal especially in endurance athletes

Front 57

What nerve has projections on the SA and AV node (predominantly)?

Back 57

Vagus nerve

Front 58

The sympathetic nerve fibers innervate both ____________(predominanlty) and to some (very little) extent _______________.

Back 58

Cardiac muscle, pacemaker cells

Front 59

What is responsible for the interactions between the sympathetic and parasympatheic systems?

Back 59

Interneuronal mechanisms

Front 60

Sympathetic (NE) neurons (inhibit/stimulate) the heart, while parasympathetic (Ach) neurons (inhibit/stimulate) the heart.

Back 60

Stimulate, inhibit

Front 61

Which neurons cause positive chronotropic (↑HR) , dromotropic (↑ conduction velocity of electrical impulses) and ionotropic (↑ contractile forces) effects?

Back 61

Sympathetic (NE) neurons

Front 62

Which neurons cause negative chronotropic, dromotropic, and ionotropic effects?

Back 62

Parasympathetic (Ach) neurons

Front 63

Doing what to the pacemaker cells in the SA and AV nodes reduces heart rate?

Back 63

Decreasing firing frequency

Front 64

How can firing frequency be reduced?

Back 64

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)

Front 65

What decreases I(f) current in reducing steepness of phase 4 (↑ERP), sympathetic or parasympathetic?

Back 65

Parasympathetic (Ach)

Front 66

What reduces Ca++ current (ICa-T) channelsm reducing steepness of phase 4 and moving threshold more positive (↑ERP), sympathetic or parasympathetic innervation?

Back 66

Parasympathetic

Front 67

What opens G-protein coupled K+ channels, increasing K+ conductance and maxing diastolic potential more negative (hyperpolarizing membrane), sympathetic or parasympathetic stimulation?

Back 67

Parasympathetic (Ach)

Front 68

What acts through beta-1 adrenergic receptors to increase heart rate (chronotropy) (↓ERP)?

Back 68

Catecholamines

Front 69

Catecholamines __________ I(f) current in SA node, therefore increasing steepness of _________.

Back 69

Increase, phase 4

Front 70

Catecholamines __________ Ca2+ current in all myocardial cells increasing steepness of _________ and moving threshold more __________.

Back 70

Increase, phase 4, negative

Front 71

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.

Back 71

a) reduce, spontaneous depolarization
b) decrease, conduction velocity, AV
c) increase

Front 72

Blockers of the delayed rectifier K+ channel increase the length of what?

Back 72

Phase 3 repolarization

Front 73

Activation of G-protein-coupled K+-channels increases what?

Back 73

The maximal negative potential

Front 74

How does decreasing the Na+ funny current I(f) affect the slope of phase 4?

Back 74

Decreases the slope of phase 4

Front 75

What are the mechanisms that decrease the firing frequency of pacemaker cells?

Back 75

Ca2+ channel blockers
Blockers of the delayed rectifier K+ channel
Activation of G-protein-coupled K+-channels
Decreasing Na+ funny current I(f)

Front 76

What are 4 common causes of abnormal electrical activity in the heart?

Back 76

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)

Front 77

What are 2 common consequences of abnormal electrical activity in the conducting and contracting myocytes?

Back 77

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)

Front 78

Low O2 supply (atherosclerosis, stenosis, spasm) and increased O2 demands (increased myocardial contractility) can lead to what?

Back 78

Inadequate myocardial blood flow, causing myocardial hypoxia.

Front 79

Patients with what disease may develop myocardial hypoxia in response to exercise or at rest (in more severe cases)?

Back 79

Coronary artery disease

Front 80

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?

Back 80

Inadequate O2 supply

Front 81

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.

Back 81

a) Less
b) Diminish
c) Conduction velocity

Front 82

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)__________).

Back 82

a) Depolarizes
b) Fast Na+
c) Inactivated

Front 83

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?)

Back 83

a) Ca++
b) SA or AV nodes
c) false! sometimes spontaneously

Front 84

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)

Back 84

Transformation of nonpacemaker into pacemaker cells AP (from myocardial hypoxia)

Front 85

What toxin blocks the voltage-gated Na+ channels?

Back 85

Tetrodotoxin

Front 86

T/F

Many antiarrhythmic drugs increase the ERP (effective refractory period), thereby altering cellular excitability.

Back 86

True!

Front 87

Which channel blockers delay phase 3 repolarization and increase the action potential duration?

Back 87

K+ channel blockers

Front 88

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)?

Back 88

Na+ channel blockers

Front 89

Name the failure of propagation in a cardiac fiber.

Back 89

Conduction block

Front 90

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.

Back 90

Reentry

Front 91

What is the term for increased or depressed normal firing rate of pacemaker cells in the SA or/and AV nodes.

Back 91

Abnormal automaticity

Front 92

Abnormal automaticity can be caused by what?

Back 92

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

Front 93

What type of afterdepolarization occurs at the end of phase 2 or about midway phase 3 (ionic mechanism is not clearly understood)?

Back 93

Early afterdepolarization (EAD)

Front 94

What type of afterdepolarization occurs at the end or just after full repolarization ( associated with elevated [Ca++]i)?

Back 94

Late afterdepolarization (LAD)

Front 95

What are 3 reasons for tachycardia?

Back 95

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).

Front 96

What are 2 reasons for bradycardia?

Back 96

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

Front 97

An ECG measures electrical difference between two of what?

Back 97

Surface electrodes placed near the heart

Front 98

ECG is a measure of what two variables?

Back 98

Voltage and time

Front 99

In an ECG, what are bipolar leads?

Back 99

I,II, and III

Front 100

In an ECG, what are unipolar leads?

Back 100

Unipolar:
Limbs: LA, LL, RA
Chest leads: V1-V6

Front 101

What does phase 0 (upstroke) of ventricular AP correspond to in the ECG?

Back 101

R wave

Front 102

What does phase 2 (plateau) of ventricular AP correspond to of the ECG?

Back 102

ST segment

Front 103

What does phase 3 (repolarization) of the ventricular AP corresponds to in the ECG?

Back 103

T wave (ventricular repolarization)

Front 104

What 5 structures CAN'T the ECG show electrical acitivity of?

Back 104

SA node, AV node, bundle branches, bundle of His, and Purkinje network

Front 105

What interval on an ECG does atrial depolarization and conduction through AV node occur?

Back 105

PR
(.12-.20 sec)

Front 106

What interval on an ECG does ventricular depolarization
atrial repolarization occur?

Back 106

QRS
(.08-.10 sec)

Front 107

What interval on an ECG does ventricular depolarization and ventricular repolarization occur?

Back 107

QT
(.40 - .43 sec)

Front 108

What interval on an ECG does ventricular repolarization
(QT minus QRS) occur?

Back 108

ST
(.32 sec)

Front 109

What do you use in the ECG for the heart rate?

Back 109

R-R interval (1 beat) during time interval

Front 110

What is the term for a subtle change in HR with respiratory cycle? Inspiration accelerates, expiration slows.

Back 110

Sinus arrhythmia