Physiology of Cardiac Muscle

Question 1

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

Answer 1

sarcoplasmic reticulum

Question 2

Overview of the steps of cardiac myocyte contraction

Answer 2

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

Question 3

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

Answer 3

Yes

Question 4

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

Answer 4

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

Question 5

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

Answer 5

True

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Na+ inactivation gates

Question 8

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

Answer 8

During the relative refractory period

Question 9

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

Answer 9

a Ca2+-

ATPase (SERCA)

Question 10

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

Answer 10

Four

Question 11

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

Answer 11

The sino atrial node

Question 12

Three areas of the heart where latent pacemakers can be found

Answer 12

Av node, bundle of His and Purkinje fibers

Question 13

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

Answer 13

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

Question 14

The parasympathetic nervous system has what effect on vascular smooth muscle

Answer 14

The parasympathetic nervous system dilates vascular smooth muscle

Question 15

What are the two types of cardiac muscle cells

Answer 15

Conducting/autorhythmic/pacemaker cells

Contractile cells

Question 16

Which system is responsible for heart rate and contraction strength

Answer 16

Autonomic nervous system

Question 17

Two intrinsic properties of the cardiac tissue

Answer 17

Automaticity and Rhythmicity

Question 18

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

Answer 18

SA node
interatrial pathways
AV node
HIS bundle
Bundle branches
Purkinje fibers

Question 19

What are the two types of cardiac action potentials

Answer 19

Fast response and slow response

Question 20

Fast response action potentials occur where in the heart

Answer 20

Atria, ventricles and purkinje fibers

Question 21

Slow response action potentials occur where in the heart

Answer 21

SA node and AV node

Pacemaker tissues

Question 22

Which ion contributes the most toward cardiac muscle membrane potential

Answer 22

K+

Question 23

What are the characteristics of fast response action potentials

Answer 23

Long duration
Plateau
Stable resting membrane potential

Question 24

what happens during phase 0

Answer 24

Rapid depolarization due to the increase in sodium conductance

Question 25

what happens in phase 1

Answer 25

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

Question 26

what happens in phase 2

Answer 26

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

Question 27

What type of calcium channels open during phase 2

Answer 27

L-type

Question 28

What happens in phase 3

Answer 28

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

Question 29

What happens in phase 4

Answer 29

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

Question 30

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

Answer 30

Na+/K+ pump, Na+/Ca2+ | antiport and Ca ATPase

Question 31

Three features of a slow response action potentials

Answer 31

has automaticity unstable resting membrane potential no plateau

Question 32

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

Answer 32

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

Question 33

What happens in phase 3 of slow response action potentials

Answer 33

repolarization is caused by potassium conductance increasing and potassium flowing out

Question 34

Which phase is the longest in slow response action potentials

Answer 34

Phase 4

Question 35

Which channel facilitates spontaneous depolarization in slow response action potentials

Answer 35

Sodium "funny" channels

Question 36

Pacemaker cell frequency may be varied by what three things

Answer 36

The rate of depolarization during phase 4 The maximal negativity during phase 4 The threshold potential

Question 37

What is overdrive supression

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What is the chronotropic effect

Answer 39

Effects of the autonomic nervous system on heart rate

Question 40

What acts in the sympathetic effect on heart rate

Answer 40

β1 receptor coupled with Gs protein and adenylyl cyclase

Question 41

What acts in the parasympathetic effect on heart rate

Answer 41

M2 receptor coupled with Gi protein

Question 42

What are the different refractory periods

Answer 42

Absolute, Effective, Relative and Supranormal

Question 43

Benefits of refractory period

Answer 43

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

Question 44

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

Answer 44

I Ca , I K , and I f

Question 45

What is the conduction velocity in the SA and AV node

Answer 45

0.05m/s

Question 46

What is the intrinsic pacemaker rate of the AV node

Answer 46

40 beats/min

Question 47

What is the intrinsic pacemaker rate of the purkinje fibers

Answer 47

20 beats/min

Question 48

What is the conduction velocity in the sinoatrial node

Answer 48

4 m/s

Question 49

Which nodal tissue is classified tertiary pacemakers

Answer 49

Purkinje fibers

Question 50

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

Answer 50

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

Question 51

Which band conducts to left atrium from the SA node

Answer 51

Anterior interatrial myocardial band (Bachmann's bundle)

Question 52

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

Answer 52

AV node

Question 53

Why is the The AP duration in atrial myocytes less

Answer 53

because efflux of K + is greater during the plateau

Question 54

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

Answer 54

I f

Question 55

extrinsic factors that can increase conduction velocity of the heart

Answer 55

sympathetic stimulation muscarinic receptor antagonists 1-adrenoreceptor agonist circulating catecholamines hyperthyroidism

Question 56

extrinsic factors that can decrease conduction velocity of the heart

Answer 56

parasympathetic stimulation muscarinic receptor agonists beta blockers ischemia/hypoxia Na and Ca channel blockers

Question 57

Examples of positive inotropic agents

Answer 57

Calcium Sympathetic stimulation & Catecholamines Increased HR

Question 58

Examples of negative inotropic agents

Answer 58

Parasympathetic stimulation

Question 59

What shape is the length tension curve of cardiac muscle

Answer 59

parabolic

Question 60

What is Frank Starling's law

Answer 60

Force generation is proportional to initial length or preload