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NSCC 7150 > The Conduction System > Flashcards

The Conduction System Flashcards

1
Q

describe mechanical cells

A
  • also known as myocardial cells
  • primary fx is contraction. contract by receiving electrical stimulus from electrical cells
  • make up bulk of heart tissue
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2
Q

define extensibility

A

ability of muscle fibers to stretch

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3
Q

describe electrical cells and their function

A
  • pacemaker cells
  • generate an electrical stimulus or impulse and conduct it down the conduction system
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4
Q

what properties do electrical cells have?

A

RACER
1) rhythmicity
2) automaticity
3) conductivity
4) excitability
5) refractoriness

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5
Q

define automaticity

A

ability of pacemaker cell to generate an electrical impulse spontaneously without external stimulation

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6
Q

define excitability

A

ability of a pacemaker cell to depolarize in response to an electrical stimulus

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7
Q

define refractoriness

A

period during which pacemaker cells are unresponsive to any stimulus, regardless of strength

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8
Q

define rhythmicity

A

ability of pacemaker cells to fire at regular intervals

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9
Q

define conductivity

A

the spread of electrical activity from one specialized pacemaker cell to another

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10
Q

what does contractility do for mechanical cells?

A

enables them to shorten and return to original length. it is dependent on the relationship between electrical and mechanical cells

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11
Q

excitation-contraction coupling

A

myocyte electrical activation leads to mechanical contraction

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12
Q

what is the purpose of the cardiac conduction system?

A

to maintain a regular and orderly sequence of electrical events that result in myocardial contraction

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13
Q

what does the conduction system consist of?

A

SA node, internodal tracts/pathways, AV node, bundle of His, R+L bundle branches, Purkinje fibers

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14
Q

SA node
- function
- location
- rate of firing

A
  • primary pacemaker of the cell
  • in the superior portion of R atrium close to where SVC enters
  • electrical impulses begin here at rate of 60-100x/min
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15
Q

what are important properties of electrical cells in the SA node?

A

automaticity and rhythmicity

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16
Q

internodal tracts
- location
- function

A
  • 3 pathways in R atrium connecting SA node to AV node
  • anterior, posterior and middle tract
  • allow rapid conduction of impulses from SA node to AV node
17
Q

AV node
- location
- function

A
  • on floor of R atrium above tricuspid valve
  • delays conduction of impulses from SA node allowing atria to contract and atrial kick to occur
  • cannot generate impulses, but in junctional tissue b/w AV node and bundle of His are some cells with electrical impulse forming properties of automaticity
18
Q

what happens if SA node fails?

A

junctional pacemaker cells can take over as secondary pacemaker site, but only fire at 40-60x/min

19
Q

bundle of His

A
  • arises from AV junction and passes in interventricular septum, dividing into bundle branches
20
Q

bundle branches

A
  • R bundle branch travels down right side of septum and branches over R ventricle, terminating in purkinje fibers on surface of R ventricle
  • L bundle branch travels down L side of septum and divides into 2 branches/fascicles (anterior and posterior) and terminates in purkinje fibers
21
Q

purkinje fibers

A
  • form a network across R+L ventricles
  • pacemaker cells in network passes electrical impulse-forming properties or automaticity
  • will fx as pacemakers if both SA node and junctional tissue pacemaker sites fail
  • rate of firing would be 20-40x/min
22
Q

action potential

A

a rapid sequence of changes in voltage across a cellular membrane

23
Q

a higher concentration of ____ ions are found in the intracellular space. A higher concentration of ____ ions are found in the extracellular space.

A

K+
Ca & Na

24
Q

polarization

A
  • resting state during which no electrical activity occurs in cardiac cells
25
Q

describe the cell in a polarized state and why

A

inside is more (-) than outside because
1) K+ leaks out of cell taking positive charges away from ICS
2) Na/K pump takes 3 Na ions out of the cells but only returns 2 K ions, leaving negative charge in ICS
3) concentration of negatively charged organic protein molecules is higher in ICS than ECS

26
Q

depolarization

A
  • begins when cardiac cell receives a stimulus
  • Na ions rush through open Na membrane channels into cell, followed by Ca ions
  • as positive ions enter cell, inside becomes more positive and outside negative making cell in a depolarized/stimulated state
27
Q

SA node is a pacemaker site. therefore, it has the ability to ________

A

depolarize without an external stimulus, a property of automaticity unique to pacemaker cells

28
Q

what happens when the SA node depolarizes?

A

depolarization travels down conduction system, and when it reaches mechanical cells stimulating cardiac muscle fibers, myocardial contraction occurs (excitation-contraction coupling)

29
Q

repolarization

A
  • results from efflux of K outside of cell through K channels
  • when inside of cell becomes more +, it triggers efflux of K ions
  • for a cell to be able to conduct another electrical impulse/depolarize, it must return to resting state
  • Na/K pump restores Na and Ca ions outside of cell and K into cell, making negative charge again so cell is ready to depolarize
30
Q

what is the clinical significance of action potentials?

A

1) ECG shows action potentials in heart
2) helps one understand actions of cardiac meds

31
Q

what are refractory periods and what are the phases?

A
  • inability to respond to a stimulus
  • absolute, relative and supernormal/vulnerable
32
Q

absolute phase

A
  • occurs during depolarization and early repolarization
  • can’t respond to any stimulus regardless of strength
33
Q

relative phase

A
  • occurs at end of repolarization
  • cell can respond to a stronger than normal stimulus bc some cells are already restored to their resting state while others remain depolarized
  • dysrhythmias can arise
34
Q

supernormal/vulnerable phase

A
  • during middle phase of repolarization and extends all the way to the resting state
  • minimal stimulus can elicit a response in this phase
  • dysrhythmias can arise
35
Q

what are the coronary arteries?

A

1) RCA (right coronary artery)
2) LDA (left descending artery)
3) circumflex

36
Q

RCA: what portion of the myocardium is supplied? conduction system?

A
  • r atrium and r ventricle
  • SA node in 50-60% of population, 90% of AV node
37
Q

LDA: what portion of the myocardium is supplied? conduction system?

A
  • anterior wall of L ventricle and septal wall
  • bundle branches
38
Q

circumflex: what portion of the myocardium is supplied? conduction system?

A
  • l atrium and posterior wall of l ventricle
  • SA node in 40-50% of population, 10% AV node

NSCC 7150 (7 decks)

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