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Cardiovascular System > Basic Electrophysiology > Flashcards

Basic Electrophysiology Flashcards

1
Q

Internal concentration of ions in cardiac myocyte

Na+:

K+:

Cl-:

Ca++:

A

Na+: 15mM

K+: 150mM

Cl-: 5mM

Ca++: 10-7mM

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2
Q

External concentrations of ions in cardiac myocyte

Na+:

K+:

Cl-:

Ca++:

A

Na+: 145mM

K+: 5mM

Cl-: 120mM

Ca++: 2mM

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3
Q

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

A

Sodium entry through the sodium channel

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4
Q

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?

A

Phase 2

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5
Q

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

A

3

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6
Q

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

A

Sodium-calcium exchanger

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7
Q

What pump maintains the concentration gradients for ions?

A

Sodium-potassium ATPase pump

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8
Q

What is the “funny channel”?

When is it activated?

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

A

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

Activated during hyperpolarization

Sodium and potassium flow into the cell

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9
Q

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

A

4; 6

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10
Q

Which subunit of the ion channels senses change in voltage?

A

S4

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11
Q

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

A

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

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12
Q

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

A

Inactivation gate

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13
Q

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

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

A

Selectivity Filter = extracellular opening of channel

Inactivation gate = cytosolic side of channel

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14
Q

What is the function of the inactivation gate?

A

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

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15
Q

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

A

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

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16
Q

Which gate of the ion channel closes first after depolarization?

A

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

17
Q

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

A

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

18
Q

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

A

Potassium: -91 mV

Sodium: +70

Calcium: +130

19
Q

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

A

1;4

20
Q

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

A

4; inward rectifying potassium current

21
Q

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

A

Slow calcium influx (and relatively low potassium efflux)

22
Q

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

A

K+ efflux

23
Q

Calcium current is primarily through what channels?

A

L-type calcium channels

24
Q

What induces Calcium release to initate contraction?

A

Calcium entry

25
Q

What two currents underlie influx of Potassium?

A

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

26
Q

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?

A

Acetylcholine binding to muscarinic receptors

27
Q

What is the primary intrinsic pacemaker?

A

SA node - spontaneous depolarization leads to action potential generation

28
Q

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

A

Gap junctions

29
Q

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

A

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

30
Q

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

Structures associated with each?

RMP for each?

Upstroke velocity?

A
  • 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
31
Q

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

A

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

32
Q

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

A

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
Q

What is the function of norepinephrine released from sympathetic nerves

A

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
Q

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

A

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

35
Q

Steepness of phase 0 indicates….

Less negative RP results in…

A

Speed of depolarization

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

36
Q

What are some changes assoacated with factors that influence action potential

Temperature:

Electrolyte Imbalance:

Hyperkalemia:

Hypokalemia:

Hypercalcemia:

Hypocalcemia:

A

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
Q

Actions associated with…

P-wave:

QRS complex:

T wave:

PR:

QT:

A

P-wave: atrial depolarization

QRS complex: ventricular depolarization

T wave: Ventricular repolarization

PR: AV node conduction

QT: Ventricular depolarization and repolarization

38
Q

Functions of Beta Blockers (block NE from sympathetic nerve)

A
  • Prevent calcium entry into cell
  • Decrease HR, conduction velocity, strength of contraction
  • Used to treat CVS conditions (hypertension, MI, Arrhythmias)
39
Q

Calcium Channel blockers used for…

A

Angina

Hypertension

Arrhythmias

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

Cardiovascular System (35 decks)

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