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Cardiovascular > The molecular mechanics of cardiac contraction > Flashcards

The molecular mechanics of cardiac contraction Flashcards

1
Q

main components of myocardium

A

contractile tissue, connective tissue,
fibrous frame,
specialised conduction system

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2
Q

what does the pumping action of the heart depend on?

A

pumping action of the heart depends on interactions between contractile proteins in its muscular walls

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3
Q

what do the interactions do?

A

interactions transform the chemical energy derived from ATP into the mechanical work that moves blood

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4
Q

how are contractile proteins activated?

A

signalling process called excitation-contraction coupling

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5
Q

when does excitation-contraction coupling begin and end?

A

begins when action potential depolarises the cell

ends when ionised calcium (Ca2+) that appears within the cytosol binds to the Ca2+ receptor of the contractile apparatus

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6
Q

movement of Ca2+ into cytosol

A

passive (downhill) process mediated by Ca2+ channels

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7
Q

when does the heart relax?

A

when ion exchangers and pumps transport Ca2+ uphill, out of the cytosol

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8
Q

the working myocardial cell

A

filled with cross-striated myofibrils

plasma membrane regulates excitation-contraction coupling and relaxation

plasma membrane separates cytosol from extracellular space and sarcoplasmic reticulum

mitochondria for ATP, aerobic metabolism and oxidative phosphorylation

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9
Q

myocardial metabolism

A

aerobic and anaerobic metabolism

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10
Q

aerobic metabolism

A

relies on FFA during aerobic metabolism

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11
Q

anaerobic metabolism

A

no FFA metabolism during hypoxia
metabolising glucose
producing energy sufficient to maintain survival of affected muscle without contraction

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12
Q

myofibrils

A

contractile proteins arranged in a regular array of thick and thin filaments

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13
Q

bands/lines

A

A-band
I-band
Z lines

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14
Q

A-band

A

region of the sarcomere occupied by the thick filaments

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15
Q

I-band

A

is occupied only by thin filaments that extend toward the centre of the sarcomere from the Z-lines

contains tropomyosin and troponins

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16
Q

Z lines

A

bisect each I-band

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17
Q

what is the sarcomere?

A

functional unit of the contractile apparatus

region between a pair of Z-lines

contains 2 half I-bands and one A-band

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18
Q

what is the sarcoplasmic reticulum?

A

membrane network surrounding the contractile proteins

consists of sarcotubular network at centre of the sarcomere and the subsarcolemmal cisternae (T-tubules and sarcolemma)

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19
Q

transverse tubular system

A

T tubule

lined by membrane continuous with the sarcolemma, so the lumen of the t tubules carries the extracellular space towards centre of the myocardial cell

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20
Q

what happens in contraction?

A

sliding of actin over myosin by ATP hydrolysis through the action of ATPase in the head of the myosin molecule

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21
Q

what do the myosin heads do?

A

heads form crossbridges that interact with actin, after linkage between calcium and TnC, and deactivation of tropomyosin and TnI

22
Q

what is myosin?

A

2 heavy chains also responsible for the dual heads
4 light chains
heads are perpendicular on thick filament at rest, and bend towards the centre of the sarcomere during contraction

23
Q

what is actin?

A

globular protein
double stranded macromolecular helix (G|)
both form F actin

24
Q

what is tropomyosin and what does it do?

A

elongated molecule
2 helical peptide chains
occupies each of the longitudinal grooves between the 2 actin strands

regulates interaction between other 3

25
Q

types of troponin

A

I, T, C

26
Q

troponin I

A

with tropomyosin it inhibits actin and myosin interaction

27
Q

troponin T

A

binds troponin complex to tropomyosin

28
Q

troponin C

A

high affinity calcium binding sites, signalling contraction

drives TnI away from actin, allowing its interaction with myosin

29
Q

control of the contractile cycle

A

calcium ions
troponin phosphorylation
myosin ATPase

30
Q

myosin location and salient properties

A

thick filament

hydrolyses ATP, interacts with actin

31
Q

actin location and salient properties

A

thin filament

activates myosin ATP, interacts with myosin

32
Q

tropomyosin location and properties

A

thin filament

modulates actin-myosin interaction

33
Q

troponin C location and salient properties

A

thin filament

binds Ca2+

34
Q

troponin I location and salient properties

A

thin filament

inhibits actin-myosin interaction

35
Q

troponin T location and salient properties

A

thin filament

binds troponin complex to thin filament

36
Q

Na+ channel role in excitation-contraction coupling

A

systole - depolarisation and open Ca2+ channels

37
Q

Ca2+ channel role in excitation-contraction coupling

A

systole - action potential plateau and Ca2+ triggered Ca2+ release

38
Q

Ca2+ pump (PMCA) role in excitation-contraction coupling

A

diastole - Ca2+ removal

39
Q

Na+/Ca2+ exchanger roles in excitation-contraction coupling

A

systole - Ca2+ entry

diastole - Ca2+ removal

40
Q

Na+ pump role in excitation-contraction coupling

A

diastole - repolarisation

and Na+ gradient for Na+/Ca2+ exchange

41
Q

Subsarcolemmal cisternae Ca2+ release channel role in excitation-contraction coupling

A

systole - Ca2+ release

42
Q

sarcotubular network’s Ca2+ pump (SERCA)

A

diastole - Ca2+ removal

43
Q

actin and myosin role in excitation-contraction coupling

A

systole - contraction

44
Q

troponin C role in excitation-contraction coupling

A

systole - Ca2+ receptor

45
Q

size of cardiac muscle cells

A

100um long and 20um diameter

46
Q

how are adjacent cardiac cells joined together?

A

end to end at intercalated disks - desmosomes join cells together, myofibrils attached to them. gap junctions also within them.

47
Q

how are cardiac muscle cells arranged?

A

in layers

surround hollow cavities

48
Q

depolarisation and Ca2+

A

influx of Ca2+ through specialised voltage-gated channels (L-type Ca2+ channels) - modified versions of dihydroxypiridine (DHP) receptors.

triggers release of larger amount of Ca2+ from sarcopasmic reticulum

49
Q

why is the release of Ca2+ from the SR triggered?

A

ryanodine receptors in the cardiac SR terminal cisternae are Ca2+ receptors
not opened directly by voltage channels, but by the binding of trigger Ca2+ in the cytosol

50
Q

when does contraction end?

A

when cystolic Ca2+ concentration is restored to its original low resting value by primary active Ca2+ -ATPase pumps in the SR and sarcolemma and Na+/Ca2+ countertransporters in the sarcolemma

Ca2+ exits the cell and returns to the SR via pumps, and K+ exits the cell and repolarises the membrane

Cardiovascular (11 decks)

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