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My Cardiology > Physiology of Cardiac Muscle > Flashcards

Physiology of Cardiac Muscle Flashcards

1
Q

The extra calcium from the “calcium induced calcium release” come from which organelle

A

sarcoplasmic reticulum

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2
Q

Overview of the steps of cardiac myocyte contraction

A

Extracellular Ca2+ enters myocardial cell → Ca2+
induces intracellular Ca2+ release → myocardial contraction, and finally myocardial
relaxation

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3
Q

Is the amount of intracellular calcium directly proportional to the degree of contraction in cardiac myocytes

A

Yes

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4
Q

True or false: cardiac myocytes have a shorter duration of action potential compared to skeletal muscle

A

False, it is about 150-300msec compared to skeletal muscle which is about 1-2msec

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5
Q

True or False: duration of an AP is directly proportional to duration of its refractory period

A

True

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6
Q

What is the reason for the long refractory periods of cardiac myocytes

A

to ensure the heart has enough time to fill during diastole and to
prevent tetany

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7
Q

The closed position of which gates during the absolute refractory period prevents an action potential

A

Na+ inactivation gates

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8
Q

During which degree of the refractory period can a “relatively” larger-than-normal stimulus generate a second AP

A

During the relative refractory period

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9
Q

Myocardial relaxation occurs when Ca2+ is pumped back into the SR via which enzyme

A

a Ca2+-

ATPase (SERCA)

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10
Q

How many phases of action potential are there for cardiac myocytes (excluding phase 0)

A

Four

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11
Q

Which node has an unstable resting membrane potential, no sustained plateau and exhibits automaticity

A

The sino atrial node

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12
Q

Three areas of the heart where latent pacemakers can be found

A

Av node, bundle of His and Purkinje fibers

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13
Q

The sympathetic nervous system has what effect on the following: heart rate, conduction velocity and contractility

A

The sympathetic nervous system increases heart rate, conduction velocity and contractility

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14
Q

The parasympathetic nervous system has what effect on vascular smooth muscle

A

The parasympathetic nervous system dilates vascular smooth muscle

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15
Q

What are the two types of cardiac muscle cells

A

Conducting/autorhythmic/pacemaker cells

Contractile cells

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16
Q

Which system is responsible for heart rate and contraction strength

A

Autonomic nervous system

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17
Q

Two intrinsic properties of the cardiac tissue

A

Automaticity and Rhythmicity

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18
Q

What are the 6 nodal tissues/conducting fibers of the heart

A 
SA node
interatrial pathways
AV node
HIS bundle
Bundle branches
Purkinje fibers
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19
Q

What are the two types of cardiac action potentials

A

Fast response and slow response

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20
Q

Fast response action potentials occur where in the heart

A

Atria, ventricles and purkinje fibers

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21
Q

Slow response action potentials occur where in the heart

A

SA node and AV node

Pacemaker tissues

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22
Q

Which ion contributes the most toward cardiac muscle membrane potential

A

K+

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23
Q

What are the characteristics of fast response action potentials

A

Long duration
Plateau
Stable resting membrane potential

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24
Q

what happens during phase 0

A

Rapid depolarization due to the increase in sodium conductance

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25
Q

what happens in phase 1

A

initial repolarization due to the sodium inactivation gates closing (in response to depolarization) and increase in potassium conductance (so K+ leaves the cell)

26
Q

what happens in phase 2

A

Plateau, because calcium conductance increases and so calcium goes into the cell while K+ is coming out at the same rate

27
Q

What type of calcium channels open during phase 2

A

L-type

28
Q

What happens in phase 3

A

Repolarization because calcium conductance decreases and potassium conductance increases even more.

29
Q

What happens in phase 4

A

Return to resting potential due to K+ being pumped out and Na+ & Ca+ being pumped in at low levels

30
Q

What are the three channels responsible for resting membrane potential during phase 4

A

Na+/K+ pump, Na+/Ca2+

antiport and Ca ATPase

31
Q

Three features of a slow response action potentials

A

has automaticity
unstable resting membrane potential
no plateau

32
Q

What is the difference in the cause of the upstroke in slow response action potentials versus fast response action potentials

A

The upstroke is caused by an influx of calcium rather than sodium in the slow response

33
Q

What happens in phase 3 of slow response action potentials

A

repolarization is caused by potassium conductance increasing and potassium flowing out

34
Q

Which phase is the longest in slow response action potentials

A

Phase 4

35
Q

Which channel facilitates spontaneous depolarization in slow response action potentials

A

Sodium “funny” channels

36
Q

Pacemaker cell frequency may be varied by what three things

A

The rate of depolarization during phase 4

The maximal negativity during phase 4

The threshold potential

37
Q

What is overdrive supression

A

WHen the SA node exhibits the fastest depolarization so the other pacemakers are supressed

38
Q

What are the 3 conditions under which latent pacemakers may take over pacemaker duties

A

Firing rate of SA node is decreased

Intrinsic firing rate of a latent pacemaker becomes faster than the SA node

Conduction from the SA node is blocked

39
Q

What is the chronotropic effect

A

Effects of the autonomic nervous system on heart rate

40
Q

What acts in the sympathetic effect on heart rate

A

β1 receptor coupled with Gs protein and adenylyl cyclase

41
Q

What acts in the parasympathetic effect on heart rate

A

M2 receptor coupled with Gi protein

42
Q

What are the different refractory periods

A

Absolute, Effective, Relative and Supranormal

43
Q

Benefits of refractory period

A

prevents tetanus

Heart can relax- prevents fatigue
Adequate time for filling before next contraction

Lasts for the entire period of systole and part of diastole

44
Q

The interactions among which three time-dependent and voltage-gated membrane currents control the intrinsic rhythmicity of the SA and AV node?

A

I Ca , I K , and I f

45
Q

What is the conduction velocity in the SA and AV node

A

0.05m/s

46
Q

What is the intrinsic pacemaker rate of the AV node

A

40 beats/min

47
Q

What is the intrinsic pacemaker rate of the purkinje fibers

A

20 beats/min

48
Q

What is the conduction velocity in the sinoatrial node

A

4 m/s

49
Q

Which nodal tissue is classified tertiary pacemakers

A

Purkinje fibers

50
Q

The interactions among which three time-dependent and voltage-gated membrane currents control the intrinsic rhythmicity of the purkinje fibers

A

I Na , I Ca , I K , and I f

51
Q

Which band conducts to left atrium from the SA node

A

Anterior interatrial myocardial band (Bachmann’s bundle)

52
Q

What is the sole entry route of the cardiac impulse to the ventricles

A

AV node

53
Q

Why is the The AP duration in atrial myocytes less

A

because efflux of K + is greater during the plateau

54
Q

What which current does the ventricles lack that makes them not have pacemaker activity

A

I f

55
Q

extrinsic factors that can increase conduction velocity of the heart

A

sympathetic stimulation

muscarinic receptor antagonists

1-adrenoreceptor agonist

circulating catecholamines

hyperthyroidism

56
Q

extrinsic factors that can decrease conduction velocity of the heart

A

parasympathetic stimulation

muscarinic receptor agonists

beta blockers

ischemia/hypoxia

Na and Ca channel blockers

57
Q

Examples of positive inotropic agents

A

Calcium

Sympathetic stimulation & Catecholamines

Increased HR

58
Q

Examples of negative inotropic agents

A

Parasympathetic stimulation

59
Q

What shape is the length tension curve of cardiac muscle

A

parabolic

60
Q

What is Frank Starling’s law

A

Force generation is proportional to initial length or preload

My Cardiology (21 decks)

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