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physiology IV > cardiac muscle mechanics > Flashcards

cardiac muscle mechanics Flashcards

1
Q

do T tubules exist in cardiac muscle?

A

yes, they invaginate at the z-line

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2
Q

what is cardiac muscle called a “functional syncytium”?

A

because all the cardiac muscle cells are mechanically and electrically connected to one other- the entire tissue resembles 1 giant cell

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3
Q

why does cardiac muscle sarcoplasm have large numbers of mitrochondria and abundant reserves of myoglobin?

A

because the cells are dependent on aerobic metabolism to obtain energy needed to continue contracting

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4
Q

does this statement describe skeletal or cardiac muscle

“physical attachment between L type calcium channel and ryanodine receptors (the endfeet)”

A

skeletal muscle

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5
Q

how are the ryanodine receptors opened in cardiac muscle cells?

A

calcium induced calcium release

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6
Q

how long does a skeletal AP last? a cardiac AP?

A

skeletal- less than 5 msec

cardiac- around 250msec

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7
Q

can there be summation in cardiac muscle action potentials?

A

NO! the refractory period prevents it- heart contracts ONLY by twitch

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8
Q

what triggers phase 1 in a ventricle action potential?

A

closing of the Na+ channels

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9
Q

what 2 stages in ventricle action potential correspond to the absolute refractory period?

A

phase 1 & 2

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10
Q

how does phase 1 look on the graph?

A

slight dip (brief repolarization)

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11
Q

how does phase 2 look on the graph?

A

plateau phase

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12
Q

how do action potentials move between adjacent cells?

A

by means of charge displacement through gap junctions

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13
Q

what percentage of the necessary calcium for a twitch in a cardiac cell comes from outside the cell?

A

20%

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14
Q

what percentage of the necessary calcium for a twitch in a cardiac cell comes from the SR in the cell?

A

80%

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15
Q

how much external calcium contributes to skeletal muscle transients and twitch?

A

ZERO percent

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16
Q

what method of calcium extraction from the sarcoplasm contributes the greatest to calcium removal?

A

sarcoplasmic and endoplasmic retiuculm ATPase (SERCA)

about 80%

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17
Q

what percentage of sarcoplasmic calcium is removed via the sodium/calcium exchanger (NCX)?

A

15%

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18
Q

besides NCX and SERCA what is the last “major” way to get ride of calcium in the sarcoplasm?

A

PCMA-pump that removes calcium from the cell

5%

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19
Q

in cardiac muscle, where does calcium bind to initiate the crossbridge cycle?

A

troponin C

20
Q

when is the twitch in a cardiac muscle terminated?

A

when there is calcium clearance from the sarcoplasm

21
Q

in cardiac muscle is there recruitment?

A

NO

22
Q

how long is the refractory period in an cardiac muscle cell action potential

A

300 msec

23
Q

what are two ways tension can be affected in cardiac muscle cells?

A
  • by altering the sarcoplasmic [ca]-by an inotropic agent

- altering calcium sensitivity of the myofilament

24
Q

withOUT vagal stimulation, what is the heart rate triggered spontaneously by the SA node?

A

100 bpm

25
Q

with vagal stimulation, what is the heart rate triggered spontaneously by the SA node?

A

60 bpm

26
Q

at what sarcomere length is the maximal force generated in the human heart?

A

2.2 micrometers

27
Q

an increase in initial length in cardiac muscle will do what to PO (maximum load)?

A

increase it

28
Q

an increase in initial length in cardiac muscle will do what to velocity of shortening? amount of shortening?

A

increase both

29
Q

an increase in initial length in cardiac muscle will do what to work the heart does? power delivered by the heart?

A

increase both

30
Q

what is unique to cardiac muscle compared to skeletal muscle regarding muscle tension?

A

in cardiac muscle there is an additional mechanism that plays a role in tension besides just myosin/actin overlap

31
Q

what results in greater sarcomere stretching?

A

greater ventricle filling during diastole

32
Q

what is the result of greater sarcomere stretching?

A

increased troponin C affinity for calcium–>more crossbridge formation per AP–> greater force of contraction during systole

33
Q

how do inotropic agents increase force of contraction?

A

by increasing the amount of calcium release from the SR

34
Q

in the heart what type of receptor does norepi bind to?

A

beta 1 adrenergic receptor

35
Q

when NE binds to a beta 1 adrenergic receptor what 4 things increase?

A

cAMP
PKA
calcium
tension

36
Q

after the administration of norepi how many beats does it usually take for the heart to reach its new steady state?

A

8 beats

37
Q

how does norepi shorten twitch duration?

A

by accelerating the SR calcium uptake pump and calcium removal from the sarcoplasm

38
Q

what does an increase in contractility do to twitch duration?

A

it decreases it

39
Q

what is the result of PKA phosphorylating phospholamban?

A

increases SR Ca++ pump sensitivity which increases the rate of Ca+ uptake into the SR and therefore decreasing duration of muscle contraction

40
Q

what are the two results of positive inotropic effects of beta adrenergic stimulation?

A

increased magnitude of contraction

decreased twitch duration

41
Q

what is the positive chronotropic effect of beta adrenergic stimulation?

A

increased HR

42
Q

what are the two ways to increase sensitivity of contractile apparatus to calcium?

A
  1. use of certain drugs

2. increase initial fiber length (starling mechanism)

43
Q

how would the curve be shifted in a tension vs calcium graph when NE is added?

A

the actual curve would not be shifted up but instead the muscle response would be shifted along the calcium tension curve

graph shown on page 369 of notes

44
Q

would the curve be shifted in a tension vs length graph when NE is added? if so, which way?

A

YES the whole curve would be shifted up

graph shown on page 397 of notes

45
Q

what is the effect on isotonic contraction of NE in the muscle?

A

isotonic contraction shortens twice the distance with the same load.
-the same contraction performed twice the work with NE

physiology IV (40 decks)

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