Basic Electrophysiology Flashcards Preview

Cardiovascular System > Basic Electrophysiology > Flashcards

Flashcards in Basic Electrophysiology Deck (39):
1

Internal concentration of ions in cardiac myocyte

Na+:

K+:

Cl-:

Ca++:

Na+: 15mM

K+: 150mM

Cl-: 5mM

Ca++: 10-7mM

2

External concentrations of ions in cardiac myocyte

Na+:

K+:

Cl-:

Ca++:

Na+: 145mM

K+: 5mM

Cl-: 120mM

Ca++: 2mM

3

What is responsible for the zero phase (upstroke) of the action potential in nonpacemaker cells?

Sodium entry through the sodium channel

4

At what phase of the Purkinje fiber and muscle cell action potential does calcium enter the cell through calcium channels causing depolarization of pacemaker cells?

Phase 2

5

Potassium exits through a potassium channel to repolarize the cell during phase __ of the AP

3

6

What exchanger channel helps maintain the low intracellular calcium concentration during resting potential?

 Sodium-calcium exchanger

7

What pump maintains the concentration gradients for ions?

Sodium-potassium ATPase pump

8

What is the "funny channel"? 

When is it activated?

What ions are involved and in which direction do they flow?

The funny channel is the HCN (Hyperpolarization-activated cyclic nucleotide-gated) pacemaker current

Activated during hyperpolarization

Sodium and potassium flow into the cell

9

How many domains do ion channels have? How many membrane spanning sections?

4; 6

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10

Which subunit of the ion channels senses change in voltage?

S4

11

What is the function of the selectivity filter on ion channels?

The selectivity filter determines the ion that can pass through the channel

12

In the sodium channel, the loop connecting domains III and IV serves ats the channel's ______ ____

Inactivation gate

13

On what side of the ion channel is the selectivity filter?

On what side of the ion channel is  the inactivation gate?

Selectivity Filter = extracellular opening of channel

Inactivation gate = cytosolic side of channel

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14

What is the function of the inactivation gate?

Another level of regulation (an intermediate state between open and closed)

15

In the resting state which part of the ion channel is still open? Why doesn't this allow Na+ ions to pass through?

Inactivation gate is still open; Na+ ions cannot easily pass through because the activation gate is still closed

16

Which gate of the ion channel closes first after depolarization?

The inactivation gate - putting the cell in to an inactive state

17

Resting membrane potential of the cardiac cell lies closest to which ions membrane potential? Why?

Potassium; this is because unlike for sodium and calcium, potassium channels are open at rest

18

What is the equilibrium potential of potassium? Sodium? Calcium? 

Potassium: -91 mV

Sodium: +70

Calcium: +130

19

Sodium channels rapidly inactivate in phase ___ of the action potential and are not recruited again until after phase ___

1;4

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20

The resting potential is represented by phase __ of the AP. What current is this phase associated with?

4; inward rectifying potassium current

21

What contributes to the plateau phase of the action potential (phase 2)?

Slow calcium influx (and relatively low potassium efflux)

22

The final rapid repolarization in phase 3 largely results from what?

K+ efflux

23

Calcium current is primarily through what channels?

L-type calcium channels

24

What induces Calcium release to initate contraction?

Calcium entry

25

What two currents underlie influx of Potassium?

IKR a rapid component and IKS a slow component - IK slowly activates but does not inactivate

26

What regulates G-protein activated K+ current in SA and AV nodal cells that decrease pacemaker rate and slow conduction rate through the AV node?

Acetylcholine binding to muscarinic receptors

27

What is the primary intrinsic pacemaker?

SA node - spontaneous depolarization leads to action potential generation

28

What are the electrical synapeses connecting cardiac myocytes permitting flow of intracellular current from cell to cell?

Gap junctions

29

His-Purkinje fibers originate at ____ ______ and split to form _____ and _______

AV node; LBB (Left bundle branch) and RBB (Right bundle branch)

30

What are differences between slow-nodal and fast non-nodal cardiac action potentials?

Structures associated with each?

RMP for each?

Upstroke velocity?

 

  • Structures associated with each?
    • Slow - SA and AV nodal cells
    • Fast - Atrial, ventricular muscle cells and Purkinje fibers
  • RMP for each?
    • Slow: -40 to -70 mV
    • Fast: -80 to -90 mV
  • Upstroke velocity?
    • Slow: 1-10V/sec
    • Fast: >100/500V/sec

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31

What may explain the relatively slow time course and automaticity of AP in pacemaker cells?

Absence of Na+ channels and presence of spontaneously opening slow Ca++ channels

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32

Function of ACh released from vagus nerve onto SA and AV node?

ACH decrease "funny current" in SA node reducing steepness of phase 4

Increases K+ conductance making the diastolic potential more negative

Slows conduction velocity

33

What is the function of norepinephrine released from sympathetic nerves

Acts on ß-adrenergic receptors in SA and AV nodes

Increases "funny channel" and steepness of phase 4

Makes threshold more negative

Does not effect maximum diastolic potential

Increases Calcium influx, stimulate SERCA (increasing stores of calcium for release)

34

What is the difference between the absolute RP (refractory period), effective RP and relative RP?

During absolute RP the cell is unexcitable to stimulation

The effective RP is a brief time beyond the absolute RP during which stimulation produces a localized depolarization that does not propagate

During the relative RP stimulation produces a weak action potential that propagates, but more slowly than usual curve

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35

Steepness of phase 0 indicates....

Less negative RP results in...

Speed of depolarization 

Slower rise of phase 0 and lower maximum amplitude of the action potential

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36

What are some changes assoacated with factors that influence action potential

Temperature:

Electrolyte Imbalance:

Hyperkalemia:

Hypokalemia:

Hypercalcemia:

Hypocalcemia:

Temperature - increase in body temp increases SA node firing

Electrolyte imbalance - Imbalance of K+ and Ca++ can have serious effects

Hyperkalemia - Raises the resting potential; slows conduction - reduction of P wave amplitude

Hypokalemia - Decrease in resting potential - flattening of T wave

Hypocalcemia and Hypercalcemia - alter myocardial AP duration (Hyper shortens ST segment and QT interval; Hypo prolongs)

37

Actions associated with...

P-wave:

QRS complex:

T wave:

PR:

QT:

P-wave: atrial depolarization

QRS complex: ventricular depolarization

T wave: Ventricular repolarization

PR: AV node conduction

QT: Ventricular depolarization and repolarization

38

Functions of Beta Blockers (block NE from sympathetic nerve)

  • Prevent calcium entry into cell
  • Decrease HR, conduction velocity, strength of contraction
  • Used to treat CVS conditions (hypertension, MI, Arrhythmias)

39

Calcium Channel blockers used for...

Angina

Hypertension

Arrhythmias

*decrease entry of calcium and delay the depolarization of SA and AV nodal cells