Cardiac Electrophysiology

Question 1

When is the cardiac membrane most permeable to potassium?

Answer 1

At rest

Question 2

What happens in a cardiac cell when the Sodium Potassium Pump is inhibited?

Answer 2

RMP becomes less negative
Cell hyperpolarizes
Cell becomes more excitable

Question 3

What are the four phases of a normal cardiac action potential?

Answer 3

Phase 4 - RMP
Phase 0 - Rapid Upstroke
Phase 1 - Partial Repolarization
Phase 2 - Plateau
Phase 3 - Repolarization
Phase 4 - RMP

Question 4

What happens to fast sodium channels during phase 1 of the cardiac musclr action potential?

Answer 4

They inactivate

Question 5

When is the cardiac muscle membrane most permeable to Sodium?

Answer 5

Phase 0

Question 6

When is the cardiac muscle membrane most permeable to Calcium?

Answer 6

Phase 0

Question 7

What is the pathway of a Fast Na+ Channel?

Answer 7

Voltage of the membrane increases
Activation gate is activated and opens Fast Na+ channel
Na+ Enters channel
High membrane voltage triggers inactivation gate
Channel closes

Question 8

What happens to the action potential of a cardiac muscle given tetrodotoxin?

Answer 8

Phase 0 is eventually lost and the Fast Na+ channel is blocked

Question 9

How does Diltiazem affect cardiac muscle?

Answer 9

It blocks L=Type Ca2+ channels and shortens phase 2
Lacl of Ca2+ causes contraction to weaken

Question 10

What is important for contraction during phase 2?

Answer 10

influx of Ca2+ ions

Question 11

What is the purpose of the ARP?

Answer 11

Long ARP protects the cardiac muscle from tetanus because it prevents another AP from firing

Question 12

In cardiac muscle, what occurs first, Mechanical activity or Electrical activity?

Answer 12

Electrical activity proceeds mechanical activity

Question 13

Which parts of the cardiovascular system experience fast response?

Answer 13

Atrium
Ventricle
Purkinje FIbers

Question 14

Which parts of the cardiovascular system experience slow response?

Answer 14

SA Node
AV Node

Question 15

Why is the atrium AP different fron the ventricle and purkinje AP?

Answer 15

Atrium generates less force and ha a shorter phase 2

Question 16

Which node is the typical pacemaker?

Answer 16

SA Node

Question 17

What happens if the SA Node cannot function properly as the pacemaker?

Answer 17

The AV Node will take over

Question 18

Where is the SA Node located?

Answer 18

Between the Super Vena Cave and Atrium

Question 19

Where is the AV Node located?

Answer 19

Between the Atrium and Ventricle

Question 20

What is the difference between fast response and slow response tissues?

Answer 20

Fast Response Tissues have Fast Na+ Channels
Slow responsse do not

Question 21

Why is the SA Node the dominate pacemaker?

Answer 21

The SA Node has the highest rate of depolarization

Question 22

What causes Phase 0 in SA Nodal cells?

Answer 22

Increase in Ca2+ permeability

Question 23

What do If channels do in SA Nodal Cells?

Answer 23

Conduct Na+ at rest
Na+ leaks in
Ca2+ leaks out

Question 24

What causes the action potential in SA Nodal Cells?

Answer 24

SA Nodal Cells spontaneously move toward threshold and fire AP

Question 25

How does Sympathetic Stimulation from the SNS affect Cardiac Muscle?

Answer 25

SNS releases NE NE binds B1 receptors K+ permeability decreases Na+/Ca2+ permeability increase Heart Rate increases

Question 26

How does Parasympathetic Stimulation from the PSNS affect Cardiac Muscle?

Answer 26

PSNS releases ACh ACh binds M1 receptors K+ permeability increases Na+/Ca2+ permeability decrease Heart Rate decreases

Question 27

Which branch of the ANS causes cardiac muscle to reach threshold more quickly?

Answer 27

SNS

Question 28

Which ANS system dominates at rest?

Answer 28

PSNS

Question 29

What happens if you cut all ANS innervation from the heart?

Answer 29

Heart Rate increases

Question 30

What happens to heart rate when the PSNS is stimuated?

Answer 30

Heart Rate Decreases

Question 31

What happens to Heart Rate when the SNS is stimulated?

Answer 31

Heart Rate Increases

Question 32

What happens when sympathetic innervation to the heart is cut?

Answer 32

Heart rate decreases

Question 33

Whatr happens when parasympathetic innervation to the heart is cut?

Answer 33

Heart Rate Increases

Question 34

What is the normal sequence of activation for cardiac muscle electrical activity?

Answer 34

SA Node -> Atrial Myocardium -> AV Node -> AV Bundle -> Bundle Branches -> Purkinje Network -> Ventricular Myocardium

Question 35

Which node has the slowest conduction velocity?

Answer 35

AV Node

Question 36

What are the requirements for reentry?

Answer 36

Unidirectional Block The absolute refractory period of the reentered tissue must be shorter tan the propagation time around the reentry loop

Question 37

Why is Ca2+ important in the heart?

Answer 37

The heart is highly dependent on extracellular Ca2+ for contractile function

Question 38

Why would tetanus be bad in the heart?

Answer 38

No blood could be pumped during tetanus

Question 39

Which refractory period prevents any stimulus, no matter how strong, from generating an action potential?

Answer 39

ARP

Question 40

How does the RRP affect the action potential?

Answer 40

It would have a lower amplitude than normal and a reduced rate of rise due to the fast Na+ channels not being completely reset and the gradients fully reestablished

Question 41

What in is responsible for the pacemaker activity in SA Nodal cells?

Answer 41

The unstable resting membrane potential of the cells

Question 42

What causes the prepotential in SA Nodal Cells?

Answer 42

The cells are more permeable to Na+ at rest (RMP) and they exhbit a gradual decline in the K+ conductance through their cell memrbanes

Question 43

What factors produce the SA Nodal prepotential?

Answer 43

Increased Na+ conductance at rest Gradually decreasing K+ conductanc Slow Ca2+ influx

Question 44

How do you slow the pacemaker discharge?

Answer 44

Decrease rate of depolarization Hyperpolarize the cell Change threshold potential

Question 45

What are the components of the conduction system?

Answer 45

SA Node Atrial internodal pathways AV Node Bundle of His or AV Bundle Bundle Branches Purkinje System Ventricualr Muscle

Question 46

How does the SA Node spread impulses?

Answer 46

Impulses move out of the SA node through the internodal pathways to the AV Node

Question 47

Where does the main delay of SA Node impulses occur?

Answer 47

In the AN Zone of the AV Node

Question 48

How does the sympathetic nervous system affect the AV node?

Answer 48

Increases conduction velocity

Question 49

How does the parasympathetic system affect the AV Node?

Answer 49

Decreases conduction velocityin AV Node

Question 50

Why is the AV Node a critical region for heart block development?

Answer 50

Under normal conditions, it is the only region where impulses from the atria can get to the ventricles

Question 51

Sumarizes the process of Excitation-contraction coupling and uncoupling...

Answer 51

1. Voltage-depedent calcium influx 2. Calcium release from SR 3. Removal of calcium from cytosol 4. b-receptor activation (catecholamines) 5. Action of cardiac glycosides (digitalis) 6. Excitation-contraction uncoupling

Question 52

What are the mechanisms of calcium release in cardiac cells?

Answer 52

Ca induced Ca release Charge movement coupled Ca release IP3 induced Ca release

Question 53

Which of the following statements regarding the autonomic nervous system is correct: A. Parasympathetic activity increases the membrane permeability to K+ B. Sympathetic innervation decreases the slope of the pacemaker potential C. Sympathetic innervation decreases the membrane permeability to Na+ and Ca2+ D. The heart will stop beating if it is denervated E. The heart rate will decrease significantly if the heart is denervated

Answer 53

A. Parasympathetic activity increases the membrane permeability to K+

Question 54

Which of the following is MOST responsible for phase 0 of the SA Nodal Phase: A. Pacemaker Channels B. Voltage-gated Ca2+ channels C. Tetrodotoxin-sensitive Na+ channels D. K+ leak Channels Cl- Channels

Answer 54

B. Voltage-gated Ca2+ channels

Question 55

Which one of the following would increase the rate of phase 4 depolarization in an SA nodal cell? A. An increase in SA Nodal K+ conductance B. Stimulation of cardiac muscarinic receptors C. Stimulation of the vagus nerve D. Increasing levels of circulating epinephrine

Answer 55

D. Increasing levels of circulating epinephrine

Question 56

In the normal heart, premature re-excitation of myocytes is prevented by: A. Gating properties of the gap junctions within the intercalated disks B. Offsetting multiple reentry mechanisms C. The ARP of the myocardial cells D. Rapid re-setting (h-gates open; m-gates close) of the voltage-gated, fast sodium channels E. Overdrive Suppression of secondary pacemakers

Answer 56

C. The ARP of the myocardial cells

Question 57

During Atrial Fibrillation, the rate of ventricular depolarization depends on ... A. The firing ate of the SA node B. The refractory period of cells in the AV node C. The conduction velocity in the atrial internosal tracts D. The conduction velocity of the Purkinje Gibers E. None of the above

Answer 57

B. The refractory period of cells in the AV node