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Physiology-Unit 5 > Cardiac electrophysiology > Flashcards

Cardiac electrophysiology Flashcards

1
Q

What are the two types of muscles?

A

conducting-pacemaker cells. coordinate contraction contractile-cardio myocytes

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2
Q

what are the two types of action potential and their location?

A

slow -SA and AV fast -artial muscle, purkinje fibers, ventricular muscle

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3
Q

what is the rise time?

A

initial change in the membrane potential, initially as a fast as nerve cell, but have a long plateau

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4
Q

what are the fast AP current?

A

0=Na influx 1=repolarization via K channels 2=prolonged plateau via L-TYPE Ca CHANNELS 3=Ca channels close and remaining K resets the membrane potential 4=reseting membrane potential

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5
Q

is there a refractory period for fast or slow AP?

A

Fast -absolute refractory period lasts from phases 0-2 -volrage gated Na channels need to be reset before second AP can be fired

slow -refractory period due to opening of the K channel and resetting of the Ca channels

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6
Q

what are the slow AP currents

A

0=Ca current rather than Na 1&2=not seen 3=fast due to K 4=use HCN channel (hyper polarization activated cyclic nucleotide gated channel a)this is the location of the funny current b)depolarizes to the thresh hold point of voltage gated sensitive Ca channels

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7
Q

Which cells are faster? What sets the heart rate?

A

SA>>AV SA node

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8
Q

pacemaker and contractile cells have what between them?explain its function

A

gap junctions a)conduction- synchronized allowing appropriate timing, via pathway. this determines the “shape” of contraction b)coupled together-keep the cells in=phasic, synchronously.

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9
Q

refractory period

A

the time the heart cannot respond fast-the Na channels need to reset slow-K channels are open and Ca channels are resetting

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10
Q

what assures the conduction of the signal from one site vs another?

A

coupling

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11
Q

where does the AP start in the atria vs ventricles during contraction?

A

atria=base ->apex ventricles= apex->base

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12
Q

How does the SNS and PSNS have on the heart? what are the receptors

A

SNS- B1 adrenergic, positive chronotropic, dromotropic and inotropic effects PSNS-M2 muscarinic receptor(ACh) negative chronotropic, dromotropic and minor negative inotropic effect

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13
Q

what causes the plateau in fast currents?

A

Calcium

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14
Q

what causes depolarization in fast and slow currents?

A

K

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15
Q

explain the following with reference to the SNS and PSNS of the heart 1-chronotropic 2-dromotropic 3-inotropic

A

1-chronotropic= heart rate changes ( 2-dromotropic=conduction velocity changes 3-ionotropic=changes in strength in contraction SNS- positive affect for all three: increasing heart rate, increasing velocity of contraction and increasing strength of contractions PSNS-negative affect for chronotropic and dromotropic. slight negative for ionotropic

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16
Q

what affect does PSNS have on the chronotrpic effect? Dromotropic effect? inotropic?

A

chronotropic Ach-

  • 1= reduces I-f in SA = longer phase 4
  • 2=reduce I-k in SA = shifting resting membrane potential toward a more negative value(hyper polarization?)
  • 3=reduces I-ca in SA = longer phase 4. Shift threshold value to a more positive value.

dromotropic 1=ACh

  • slows conduction- making it longer for one cell to polarize another

very weak inotropic affect

17
Q

Where does the PSNS have the greatest effect, AV or SA node?

A

SA node, b/c this node drives the heart. the AV node is affected by the AV node, but the SA node sets the sets the heart rate.

18
Q

Which locations contain the slow conducting and fast conducting cells?

A

Slow= SA and AP Fast=purkinje fibers, atrial muscles, ventricular muscles

19
Q

how do catecholamines affect the chronotroptic effect? dromotropic affect?

A

the heart rate is manipulated by catecholamines by a)increasing the I-f in the SA node= shorter phase 4(higher frequency) b)shift threshold value to a more negative value c) increase resting membrane potential by reducing I-k dromotropic a)these current changes all affect the dromotropic affect, velocity of the beats increases

20
Q

what needs to change in order for the negative/positive affect to be achieved on chronotropic, dromotropic and ionotropic effect?

A

negative= 1- PSNS- all by ACh a)reduce currents of the “f” and “ca” b)increase current of “k” positive a)increase currents of “f” and “ca” b)decrease current of “k”

21
Q

Describe what is happening during each phase of the slow AP. explain the two ways that calcium enter the cytoplasm.

A

0=Influx of Na causes depolarization. activating the voltage sensitive L-type Ca channels on the sarcolemma begin to open

1=K begins to flow out and Na channels close

2=Ca channels open. Also, the calcium induced calcium channel release channel on the SR

3=Ca channels close. K repolarizes the Vm to rest

4=cell is at resting membrane potential

There are two Ca channels - both sources of

1) Ltype voltage sensitve L-type Ca channel on the sarcolemma (extracellular)
2) CICR channel on the sarcoplasmic reticulum (intracellular)

22
Q

what is the majority of the energy produced by in cardiac muscles?

A

aerobic metabolism, an abundance of mitochondria

23
Q

how many times does a cardiomyocyte contract per heart beat?

how do catecholamines affet the myocardiocytes?

A

once!

unlike skeletal muscle, which recruit more cells (since all cells are recruited each contraction), cardio cytes increase heart beat via INOTROPIC MODULATION(Ca modulation)

inotropic modulation

  1. catecholamines=
    1. increase current of Ca, via L-type channels.
      1. this increases force
    2. increase CICR
      1. inducing greater Ca
    3. increase SERCA
      1. increase reqequestration activity
    4. increase affinity of troponin to Ca
24
Q

What are the 3/4 things that are modified by catecholamines in regars to Ca flux in cardiomyocytes?

A

Ca increase

1-Ltype channels open= increase extracellular Calcium

2-CICR increase = increasing intracellular calcim levels

3-SERCA activity increases = faster resequestration of the

4=increase affinity of troponin C to Ca

25
Q

Deflection on ECG corresponds to…

A

Depolarization of the atria/ ventricles

repolarization of the venctricles

26
Q

describe the events at each segment of the ECG. which interval gets shorter with heart rate?

A

P=indicative of the SA serving as the pacemaker. Length indicates atrial depolarization.

Pwave=depolarization of the artial muscles

PR=conduction thru AV node and to ventricles

QRS=duration tells us how fast the depolarization spreads throughout the ventricles

QT=interval releals how long the ventricles remain depolarized. gets shorter with increasing heart rate.

Twave=repolarization of both ventricles

27
Q

describe the starling law and how it applies to cardiomyocytes

A

sarcomere length where the troponin and myosin overlap determines the contraction force. There is much more fiver around the heart that resists contraction

1- tension is built up very quickly b/c of connective tissue

28
Q

what is EC coupling?

A

the process of increasing the inotropic affects on the heart via the L-type and CICR channels. increasing the Calcium channels increase the contracile force…

29
Q
  1. what delivers the parasympathetic projections to the heart and where do they influence?
  2. compare to sympatheticvagus
A
  1. vagus
    1. SA and AV nodes
  2. sympathetic
    1. cardiac muscle
30
Q

sympathetic and parasympathetic operate through what receptors?

A

sympathetic-B1

PARASYMPATHETIC= M2

Physiology-Unit 5 (10 decks)

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