Physiology - Cardiac Muscle

Front 1

what are two potential results of heart failure?

Back 1

1) Blood accumulates
behind the heart, causing the veins to be overfilled.
2) Too little blood flows out of the heart to provide for the needs of the body

Front 2

what is the "most important intracellular messenger"?

Back 2

Calcium

Front 3

what effect does calcium entry have on resting myocytes?

Back 3

it causes contraction

Front 4

does calcium enter the cell via passive or active processes?

Back 4

passive. the gradient from outside to inside is downhill.

Front 5

what must happen to the intracellular calcium for the heart to relax?

Back 5

it must be pumped out, uphill.

Front 6

how great is the Ca++ concentration gradient across the plasma membrane?

Back 6

10,000 times

Front 7

why is calcium so concentrated outside the cell?

Back 7

calcium phosphate is insoluble, and due to large amount of phosphate in cell, calcium is excluded.

Front 8

what impact on action potentials does calcium influx have on myocytes?

Back 8

causes depolarization and subsequent contraction

Front 9

which proteins in the cell bind Ca++ with high affinity?

Back 9

E-F Hand proteins

Front 10

is Ca++ diffusion enough to trigger an action potential in adult cardiac myocytes? why or why not?

Back 10

no; diffusion is too slow to alone cause a sufficient AP in adult myocytes

Front 11

where are intracellular Ca++ stores located?

Back 11

sarcoplasmic reticulum (SR)

Front 12

what is the sarcotubular network?

Back 12

part of SR that pumps Ca++ out of cytosol

Front 13

what occurs at sarcolemmal cisternae?

Back 13

electrical signals from t-tubules are transmitted to SR

Front 14

what is the name for intersection of t-tubules and sarcolemmal cisternae?

Back 14

dyads

Front 15

Why are Ca++ release channels often called 'ryanodine receptors'?

Back 15

because they bind well to ryanodine even though it has nothing to do with their function

Front 16

what is another name for ryanodine receptors?

Back 16

feet

Front 17

what is the relationship between ionic environment of t-tubules with that of the exterior of the cell?

Back 17

identical. the t-tubules are continuous with the extracellular environment

Front 18

which channels are responsible for bringing extracellular Ca++ into cell?

Back 18

L-type Calcium channels

Front 19

which 2 channels pump Ca++ from inside cell to ECF?

Back 19

1) Na+/Ca++ pump
2) Plasma membrane Ca++ pump (PMCA)

Front 20

through what channel does Ca++ exit SR into the cytosol?

Back 20

SR Ca Release Channels

Front 21

through what channel is Ca++ brought back into SR from cytosol?

Back 21

SR Ca Pump

Front 22

which channel provides the "small bang" that triggers the "large boom"?

Back 22

L-type Ca++ channels

Front 23

the Na+/Ca++ exchanger created which type of current? what is driving force of pump?

Back 23

inward current due to Na+ current; driving force is Na+ conc. gradient

Front 24

why can Na+/Ca++ exchanger cause problems in heart failure patients?

Back 24

too much Ca++ in heart of heart failure patients causes action of Na/Ca pump, creating influx of Na which could cause contractions and MI's.

Front 25

where is location of feet proteins?

Back 25

between sarcolemmal cisternae and t-tubules

Front 26

how many Ca++ 'holes' does each foot contain?

Back 26

4

Front 27

which proteins binds Ca to initiate muscle contraction?

Back 27

Troponin C

Front 28

Which ATP-dependent pump is responsible for sequestering Ca in SR?

Back 28

SERCA2a

Front 29

which protein regulates the SERCA2a channel?

Back 29

phospholamban

Front 30

which protein regulates phospholamban?

Back 30

cyclic ATP-dependent protein kinase (PK-A)

Front 31

what effect does phosphorylation have on phospholamban? phosphorylation is done in response to what?

Back 31

more complete Ca sequestration, more complete relaxation, more forceful subsequent contractions; done in response to sympathetic activation

Front 32

which protein helps to keep Ca inside SR and prevent from leaking out feet?

Back 32

Calsequestrin

Front 33

a sarcomere sits between which two points?

Back 33

z-lines

Front 34

how many A bands are present in a sarcomere? I bands?

Back 34

1 A band; 2 half-I bands

Front 35

cross-bridges in myocytes connect _______ with ________.

Back 35

thin filaments; thick filaments

Front 36

Z lines are composed mainly of which protein?

Back 36

Titin

Front 37

at rest, what is the position of cross-bridges in myocyte?

Back 37

at right angles to thick and thin filaments

Front 38

thick filaments are composed of _______. thin filaments are composed of __________.

Back 38

myosin tails; actin

Front 39

which chain of myosin, heavy or light, hydrolyzes ATP?

Back 39

heavy chain

Front 40

ATP energy is used to do what in myosin?

Back 40

used to move cross bridge and force muscles to contract

Front 41

of what are cross-bridges composed?

Back 41

myosin heads

Front 42

_______ is the name for the protein which resides in the groove between 2 actin thin filaments.

Back 42

tropomyosin

Front 43

what kind of protein is Troponin C?

Back 43

E-F Hand

Front 44

When Ca is not bound to Troponin C, ________ inhibits actin-myosin interactions

Back 44

Troponin I

Front 45

What is the role of Troponin T?

Back 45

Binds Troponin I and Troponin C to Tropomyosin

Front 46

Which protein on the thin filament is physically in the way of actin-myosin binding?

Back 46

Tropomyosin

Front 47

which, preload or afterload, is related to pressure as the ventricle is filling? which is related to ejecting pressure?

Back 47

preload - filling; afterload - ejecting

Front 48

what is the consequence of maximum afterload? of zero afterload?

Back 48

muscle cannot shorten; cross-bridges cycle at maximum rate

Front 49

when afterload is ________, internal work increases.

Back 49

increases

Front 50

maximal force is related to what factor?

Back 50

number of actin-myosin cross bridges

Front 51

Vmax is related to what factor?

Back 51

turnover rate of actin-myosin cross bridges

Front 52

Vmax is maximum at _______ afterload; maximal force is maximum at __________ afterload.

Back 52

zero; maximum

Front 53

Vmax is determined mainly by what?

Back 53

myosin heavy chain isoform

Front 54

what happens to muscle tension when muscle length is greater than max length?

Back 54

decreases.

Front 55

muscle length is determined by preload or afterload?

Back 55

preload

Front 56

optimally, does the heart operate on the ascending or descending limb of tension-length curve?

Back 56

ascending

Front 57

what is the result of an increase in venous return during descending limb of tension-length curve?

Back 57

vicious cycle

Front 58

what does the heart's 'low compliance' mean?

Back 58

it is highly stiff

Front 59

a dilated heart usually operates on which limb of the tension-length curve?

Back 59

descending

Front 60

at peak tension, what percentage of myosin and actin filaments are interacting?

Back 60

100%

Front 61

what is a change in contractility for the heart? how is this achieved?

Back 61

a change in ability to do work without directly changing preload or afterload; achieved by drugs (digitalis), sympathetic stimulation

Front 62

what is the most important way to modify contractility in myocytes?

Back 62

increase Ca binding