Cardiac Electrophysiology

Question 1

Slowly and automatically depolarize to the threshold potential at which they fire an all or none action potential

Answer 1

Pacemaker cells

Question 2

Cells involved in developing force during each contraction of the heart— they fire action potential when stimulated

Answer 2

Non-pacemaker

Question 3

Pacemaker cells are specialized myocardial cells that are located in the

Answer 3

SA and AV nodes

Question 4

Pacemakers cells are authorhythmic?

Answer 4

Yep, the spontaneously generate action potential

Question 5

Pacemaker potential- phase 4

Answer 5

Depolarization- membrane potential slowly rises to threshold in SA and AV nodes

Question 6

Step 2 is when

Answer 6

Action potential begins to fire once threshold is reached

Question 7

Step 3 is when

Answer 7

There is a repolarization to resting potential

Question 8

_____ response action potential

Answer 8

Slow

Question 9

Funny current

Answer 9

Inward slow flux of Na+ through non-specific ion channels

Question 10

Phase 4 depolarization involves 3 voltage gated membrane currents

Answer 10

1. Decrease in outward flux of K+
2. Funny current
3. Gradual inlfux of Ca2+ as threshold is approached

Question 11

Depolarization results from opening of voltage gated

Answer 11

L-type Ca2+ channels

Question 12

Repolarization results from opening of voltage gated

Answer 12

K+ channels

Question 13

The primary pacemaker in the intact heart with an intrinsic rhythm at rest of 60-100 depolarizations per minute

Answer 13

SA node

Question 14

Depolarizers at a slower intrinsic rhythm and typically receives its signal from the SA node. It acts as a secondary pacemaker that can take over regulation of the heart if the SA node is damaged

Answer 14

AV node

Question 15

Conducting network in the ventricles has an even slower intrinsic rhythm and could act as pacemakers only of the SA and AV nodes fail

Answer 15

His-purkinje fibers

Question 16

All pacemakers share the same ionic mechanism of autorhythmicity

Answer 16

Yep

Question 17

What happens when there is a parasympathetic action?

Answer 17

1. Voltage gated K+ channels close more slowly- hyper polarizes resting potential
2. Decreased funny current- reduces slope of phase 4 depolarizations
3. Decrease in Ca2+ channels in late phase

This all leads to a slow heart rate

Question 18

Parasympathetic innervation and mediator

Answer 18

Vagus n. And releases acetyl choline to SA node

Question 19

Action of sympathetic intervention on heart

Answer 19

1. Increased funny current in nodes and Ca2+ channels in all myocardial cells
2. Alters threshold toward more negative voltage

• this increases heart rate and increases force of contraction owing to increasing intracellular Ca2+ leading to a +/- inotropic effect

Question 20

Sympathetic innervation and mediator

Answer 20

Innervation is the cardiac plexus and releases Norepinephrine to SA and AV nodes and myocardium

Question 21

Non pacemaker cells true resting potential of

Answer 21

-90 mV

Question 22

Non pacemaker cells are excited by

Answer 22

APs from adjacent cells

Question 23

Phase 0

Answer 23

Rapid influx of Na+ through voltage gated channels leading to a depolarization towards ENa+

Question 24

Phase 1

Answer 24

Inactivation of Na+ channels plus opening of a transiently outward K+ channel

Question 25

Phase 2

Answer 25

Plateau phase involve an inward flux of Ca2+ through L-type. (Long lasting) voltage gated channels, balanced by a slow outward K+ current and Iks - voltage stays close to 0

Question 26

Phase 4

Answer 26

Small fluxes of Na+ and K+ maintain the resting potential

Question 27

Phase 3

Answer 27

Repolarization when Ca2+ channels close and potassium effluent, returns the membrane to resting potnetial

Question 28

Non pacemakers cells have a rapid depolarization thus they are referred to as

Answer 28

Fast response

Question 29

Period comprising phases0,1,2, and part of 3, during which a new action potential cannot be elicited

Answer 29

Effective or absolute refractory period

Question 30

Are Na+ channels inactivated during refractory period?

Answer 30

Yep

Question 31

Duration of ERP (effective refractory period) can be 100-250 msec; _____ times for atrial muscle and _____ for ventricular

Answer 31

Shorter times for atrial muscle and longer for ventricular

Question 32

Significance of ERP

Answer 32

Limits the frequency AP and prevents the heart from summing twitches or tetanizing thus allowing time for ventricular filling between beats

Question 33

In atrial and ventricular myocardium conduction of AP is primarily by cell-cell contact through

Answer 33

Gap junctions

Question 34

Gap junctions contain ______ resistance ion channels that allow depolarizing currents to spread from one cell to adjacent cells

Answer 34

Low

Question 35

Explain to me the sequence of the activation of the heart

Answer 35

1. SA node fires AP 2. Signal is conducted through the atrial muscle cell to cell 3. Signal reaches the AV node which is the only conducting pathway from the atria into the ventricles 4. Small diameter fibers within the AV node delay conduction of the impulse into the ventricular muscles 5/ fibers leaving the AV node expand and enter the ventricles at the base of the septum= bundle of His 6. Bundle of His divides into right and left brindle branches that ratify down the Endo cardinal surfaces of the septum spreading laterally 7. Bundle branch fibers divide into purkinhe fibers that spread the impulse into the ventricular myocardium to individual myocytes which then conduct via gap junction

Question 36

Junctions fibers are slow or fast acting fibers?

Answer 36

Slow that is why we see a delay in conduction into the ventricular muscle

Question 37

Spread of impulse

Answer 37

Septum—> apex—> base and endo—> epicardium

Question 38

Duration of APs is longer in _____ and ________ myocytes than in _______ myocytes

Answer 38

In bundle branches and subendocardial are longer than in subepicardial

Question 39

Who are the last to depolarize but are the first to repolarize

Answer 39

Subepicardial myocytes

Question 40

Ventricular depolarizations spreads _______ over the pathway of depolarization

Answer 40

Backwards

Question 41

Dipoles measure and record electrical changes on the

Answer 41

Outside fo the muscle strip

Question 42

Dipoles exist when there is a

Answer 42

Separation of charge along the muscle strip

Question 43

If the tissue is uniformly charge— isoelectric— how are the dipoles?

Answer 43

No dipoles exist

Question 44

When a dipole vector indicating depolarization it points toward the positive electrode the signal is

Answer 44

positive

Question 45

When a dipole vector indicating repolarization points toward the positive electrode, the signal is

Answer 45

Negative

Question 46

Electrodes placed perpendicularly to a dipole vector it shows

Answer 46

No deflection