CVS Physiology 2: Cardiac Electrophysiology And Excitation-contraction Coupling.

Question 1

List the 4 basic properties essential for the heart to function as the central pump?

Answer 1

1- autorhythmicity.
2- conductivity.
3- excitability.
4- contractility.

Question 2

Definition: generating its own electrical impulse rhythmically.

Answer 2

Autorhythmicity.

Question 3

Definition: ability to conduct electric impulse.

Answer 3

Conductivity.

Question 4

Definition: ability to respond to stimuli by producing electrical action potentials.

Answer 4

Excitability.

Question 5

Definition: a capacity for shortening in response to suitable stimulus.

Answer 5

Contractility.

Question 6

Electrical impulses are generated and conducted in the _______.

Answer 6

Heart.

Question 7

Excitation wave starts from _________ _______ (__ m/s), then to __________ ______ (__m/s), the to the ________ _______ (__ m/s), finally to ______ ____ ____ and ____ ____ _____ (__m/s).

Answer 7

Excitation wave starts from sinoatrial node (SAN) = (1m/s).
Then to atrioventricular node (AVN) = (0.05m/s).
Then to the atrioventricular bundle (AVB) = (1m/s).
Finally to:
Right bundle branch (RBB).
Left bundle branch (LBB).
(4m/s).

Question 8

Which node is the dominant node?

Answer 8

SA node “pacemaker”.

Question 9

Why does the AV node have a 100-msec delay?

Answer 9

Allows time for ventricular filling.

Question 10

List the order of pacemaker rates?

Answer 10

SA > AV > bundle of His/purkinje/ ventricles.

Question 11

List the order of the speed of conduction?

Answer 11

Purkinje > atria > ventricle > AV node.

Question 12

List the 3 ions in the resting ventricular muscle cell?

Answer 12

1- K+.
2- Na+.
3- Ca2+.

Question 13

What is the intracellular concentration of K+ in the resting ventricular muscle cell?

Answer 13

135 mEq/L.

Question 14

What is the intracellular concentration of Na+ in the resting ventricular muscle cell?

Answer 14

10 mEq/L.

Question 15

What is the intracellular concentration of Ca2+ in the resting ventricular muscle cell?

Answer 15

.0001 mEq/L.

Question 16

What is the extracellular concentration of K+ in the resting ventricular muscle cell?

Answer 16

4
(Meaning it moves from intracellularly to extracellularly).

Question 17

What is the extracellular concentration of Na+ in the resting ventricular muscle cell?

Answer 17

145
(Meaning it moves from extracellularly to intracellularly).

Question 18

What is the extracellular concentration of Na+ in the resting ventricular muscle cell?

Answer 18

2
(Meaning it moves from extracellularly to intracellularly).

Question 19

What is the equilibrium potential of K+ in the resting ventricular muscle cell?

Answer 19

-94 mV.

Question 20

What is the equilibrium potential of Na+ in the resting ventricular muscle cell?

Answer 20

+70 mV.

Question 21

What is the equilibrium potential of Ca2+ in the resting ventricular muscle cell?

Answer 21

+132 mV.

Question 22

What is the permeability of K+ in the resting ventricular muscle cell?

Answer 22

High.

Question 23

What is the permeability of Na+ in the resting ventricular muscle cell?

Answer 23

Low.

Question 24

What is the permeability of Ca2+ in the resting ventricular muscle cell?

Answer 24

Low.

Question 25

List the 3 main groups of membrane channels?

Answer 25

1- ungated channels. 2- voltage - gated channels. 3- ligand - gated channels.

Question 26

Which membrane channel is concentration based? And give an example?

Answer 26

Ungated channels. E.g: K+ channel.

Question 27

Which membrane channel is voltage dependent? And give an example?

Answer 27

Voltage - gated channel. E.g: Na+ channels, Ca2++ channels, K+ channel.

Question 28

Which membrane channel is ligand (protein) dependent? And give an example?

Answer 28

Ligand - gated channel. E.g: acetylcholine gated.

Question 29

What is the way of diffusion of ungated channels?

Answer 29

Passive diffusion.

Question 30

List the 2 types of cardiac muscle fibers?

Answer 30

1- contractile fibers. 2- excitatory and conductive fibers (auto rhythmic cells).

Question 31

What is the major cardiac muscle fiber?

Answer 31

Contractile fibers.

Question 32

Which cardiac muscle fiber is responsible for the generation and conduction of the excitation wave of all parts of the cardiac muscle?

Answer 32

Excitatory and conductive fibers (auto rhythmic cells).

Question 33

Which cardiac muscle fibers constitute the atrial and ventricular walls?

Answer 33

Contractile fibers.

Question 34

Which cardiac muscle fibers is responsible for the pumping action of the heart?

Answer 34

Contractile fibers.

Question 35

What do the excitatory and conductive fibers (auto rhythmic cells) include? (5)

Answer 35

1- SAN fibers. 2- AVN fibers. 3- bundle of His = A-V bundle. 4- Rt and Lt bundle branches. 5- purkinje fibers.

Question 36

Definition: the intracellular potential of the resting cell?

Answer 36

Resting membrane potential (RMP).

Question 37

What is the resting membrane potential (RMP) of a resting myocyte?

Answer 37

-90 mV.

Question 38

In atria and ventricular cells, the resting membrane potential is _____, until ______ _____ is applied.

Answer 38

Stable until external excitation is applied.

Question 39

In the SA node cells, membrane potential is ___ _____ and called as the ______ _______, always moving towards the ____ ____ with time.

Answer 39

Not stable and called as the pacemaker potential, always moving towards zero millivolts (mV) with time.

Question 40

Definition: negative intracellular potential moves towards zero and then becomes positive.

Answer 40

Depolarization.

Question 41

Give an example of depolarization?

Answer 41

Na+ or Ca2+ influx depolarizes cell.

Question 42

Definition: negative intracellular potential is re-established after depolarization.

Answer 42

Repolarization.

Question 43

Give an example of repolarization?

Answer 43

K+ efflux repolarizes cells.

Question 44

What effect would increasing the extracellular K+ ion has? What is the net result?

Answer 44

Reduce the efflux of K+ ions or even create an influx of K+ ions, the net result will be depolarization.

Question 45

What effect would decreasing the extracellular K+ ion has? What is the net result?

Answer 45

Accelerate the efflux of K+ ions, the net result of which will be hyperpolarization.

Question 46

A cell’s resting membrane potential is very sensitive to change in what?

Answer 46

A change in extracellular K+ ions.

Question 47

What is the response of cardiac action potential in ordinary myocytes?

Answer 47

Fast response.

Question 48

What is the response of cardiac action potential in nodal muscle fibers?

Answer 48

Slow response.

Question 49

Where does the fast response of cardiac action potential occur?

Answer 49

Occurs in atrial, ventricular muscles and purkinje fibers.

Question 50

Where does the slow response of cardiac action potential occur?

Answer 50

Occurs in the SA and AV.

Question 51

What is membrane potential of SAN?

Answer 51

SA has unstable membrane potential, (-55:-60).

Question 52

Which channels open and close with Low K and high Na? (Extracellularly)

Answer 52

Closure of K+ channels. Opening of “funny” channels (Na+ channels).

Question 53

Which channels open and close with high Ca?

Answer 53

Opening of voltage-gated Ca++ channels (transient, T-type channels). Closure of funny channels.

Question 54

Which channels open and close with high high Ca?

Answer 54

Opening of voltage-gated Ca++ channels (long, L-type channels). Closure of T-type Ca++ channels.

Question 55

Which channels open and close with high K and low Ca?

Answer 55

Opening of voltage-gated K+ channels. Closure of voltage-dependent Ca++ channels (L-type).

Question 56

List the 2 effects of parasympathetic stimulation?

Answer 56

1- hyperpolarize >> increasing conductance out of cell and decrease “funny current” (sodium) and calcium conductance. 2- decrease in the slope if pre potential >> takes longer to reach the threshold >> intrinsic firing decreases.

Question 57

List the 2 effects of sympathetic stimulation?

Answer 57

1- activation of beta receptors >> increased “funny current” (sodium) and increased calcium influx. 2- increase in the slope of prepotential >> threshold is reached sooner >> intrinsic firing increases.

Question 58

Increased Ca2+ premeability in cardiac myocytes has which effects?

Answer 58

Increased contractility and increased SV.

Question 59

What happens in phase 0 of electrical activity?

Answer 59

Depolarization of the membrane to -65 mv leads to opening of fast Na+ channels, this causes rapid influx of Na+ ions.

Question 60

What happens in phase 1 of electrical activity?

Answer 60

Brief repolarization caused by K+ efflux.

Question 61

What happens in phase 2 (plateau) of electrical activity?

Answer 61

Balance between inward Ca++ and outward K+.

Question 62

What is the importance of the plateau phase?

Answer 62

Important to maintain contraction for adequate time to empty the heart chambers.

Question 63

What happens in phase 3 of electrical activity?

Answer 63

Rapid repolarization, Causes: 1- inactivation of Ca++. 2- activation of outward K+ channels (delayed rectifier).

Question 64

What happens in phase 4 of electrical activity?

Answer 64

Causes: continuous activation of outward K+ channels.

Question 65

How long does the absolute refractory period lasts?

Answer 65

Lasts almost the entire time of one cardiac muscle twitch (one contraction).

Question 66

What happens by the time the action potential and muscle contractions are fully over?

Answer 66

No tetany of cardiac muscle possible.

Question 67

What happens when Ca++ ions enter the cardiac muscles?

Answer 67

Induces Ca++ release from sarcoplasmic reticulum.

Question 68

The heart is a syncytium of many cells electrically connected at intercalated discs by _______ _______?

Answer 68

Gap junctions.

Question 69

Cardiac muscle is _______ type and contain __ _____ and highly developed _______ ___ _______.

Answer 69

Striated type and contain T-tubules and highly developed intracellular SR networks.

Question 70

_____ _____ provide the excitation stimulus used to activate plasma membrane Ca2+ channels causing a substantial ____ ______.

Answer 70

Action potentials. Ca2+.

Question 71

Ca2+ induces Ca2+ release (CICR) through which channel?

Answer 71

Ryanodine receptor channels (RyR).

Question 72

What does local release of Ca2+ cause?

Answer 72

Causes calcium sparks.

Question 73

Calcium ion binds to what to initiate contraction?

Answer 73

Troponin.

Question 74

What occurs when calcium unbinds from troponin?

Answer 74

Relaxation.

Question 75

Ca2+ is pumped back into SR for what?

Answer 75

Storage.

Question 76

Ca2+ is exchanged with what?

Answer 76

Na+.

Question 77

Na+ gradient is maintained by what?

Answer 77

Na-K-ATPase pump.