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Physiology 1 (WPH) > L8: muscle contraction > Flashcards

L8: muscle contraction Flashcards

1
Q

T/F in a muscle contraction, thick and thin filaments shorten

A

false - they slide past each other, do not shorten

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2
Q

H band

A

myosin only portion of sarcomere

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3
Q

M line

A

line down middle of H band – where myosin separate into different polarities

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4
Q

I band

A

actin only portion of sarcomere

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5
Q

Z line

A

line down middle of I band – where actin filaments are anchored

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6
Q

A band

A

the whole myosin portion of sarcomere, including where it overlaps with actin

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7
Q

these bands of a sarcomere shorten during contraction

A

H band

I band

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8
Q

this protein anchors myosin to Z lines

A

titin

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9
Q

titin

A

anchors myosin filaments to z-lines

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10
Q

this protein lies along actin in the sarcomere and is thought to be a ruler to determine thin filament length

A

nebulin

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11
Q

nebulin

A

lies along actin in the sarcomere and is thought to be a ruler to determine thin filament length

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12
Q

a muscle fiber is encased by…

A

the sarcolemma

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13
Q

a muscle fibril is encased by…

A

sarcoplasmic reticulum

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14
Q

outline the pathway from motor neuron action potential to actin exposure in skeletal muscle

A 
motor neuron
ACh
N1 receptor
motor end plate
sarcolemma
t-tubule
DHPR dihydropyridine receptor
RYR1 ryanodine receptor
Ca++
troponin c
troponin i
troponin t
tropomyosin
exposed actin
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15
Q

outline the pathway from neuromuscular synapse to exposed actin in cardiac muscle

A 
synapse (cholinergic or adrenergic or other)
sarcolemma
t-tubule
DHPR
Ca++
RYR2
Ca++
troponin c
troponin i
troponin t
tropomyosin
exposed actin
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16
Q

how is calcium release in skeletal muscle different from calcium release in cardiac muscle?

A

skeletal - DHPR appears to directly activate the RYR1 channels to release Ca++
cardiac - DHPR releases Ca++, which activates RYR2 to release Ca++

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17
Q

DHCR in skeletal and cardiac muscle contraction is…

A

dihydropyridine receptor
in skeletal muscle - activates RYR1 Ca++ release
in cardiac muscle - releases Ca++, which binds RYR2 receptors and activates RYR2 Ca++ release

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18
Q

RYR1

A

ryanodine receptor 1

in skeletal muscle, is directly activated by DHPR protein of t-tuble and releases Ca++

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19
Q

RYR2

A

ryanodine receptor 2

in cardiac muscle, is activated by the Ca++ released by DHPR in t-tubule to release more Ca++

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20
Q

troponin c

A

binds calcium, signals troponin i to release actin, which signals troponin t to shift topomyosin and expose actin

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21
Q

troponin i

A

binds to actin to hold troponin-topomyosin complex in place

between troponin c and t

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22
Q

troponin t

A

binds tropomyosin, receives signal to shift from troponin c signal to troponin i

23
Q

how is calcium resequestered into sarcoplasmic reticulum?

A

Ca++ ATPase pump

24
Q

what protein buffers Ca++ concentrations in the SR so that more can be stored?

A

calsequestrin

25
Q

calsequestrin

A

buffers Ca++ concentrations in the SR so that more can be stored

26
Q

rigor state

A

all ATP has been hydrolyzed so M-ADP+Pi complex is stuck bound to actin

27
Q

rigor mortis occurs because…

A

all ATP has been hydrolyzed so M-ADP+Pi complex is stuck bound to actin

28
Q

a myosin molecule has _ heavy chains and _ light chains

A

2 heavy chains (binding and ATPase)

4 light chains (1 essential 1 regulatory for each heavy chain

29
Q

the pivot in myosin during crossbridge cycling occurs at this location

A

between the head and essential light chian

30
Q

what are the two myosin light chains

A

essential (closer to head)

regulatory (closer to tail)

31
Q

how many g-actin subunits per f-actin repeat?

A

13-14 (non-integral)

32
Q

in rigor, myosin heads are at a __ degree angle to actin

A

45 degree angle

33
Q

in a transverse section, thin filaments are arranged in a __ pattern about thick filaments

A

hexagonal

34
Q

how many thin filaments does one thick filament bind to?

A

6

in transverse section, thin filaments are arranged in a hexagonal pattern around thick filaments

35
Q

why do actin-myosin crossbridges cycle in an asynchronous manner during muscle contraction?

A

provide gradual shortening

prevent slippage under tension

36
Q

what is the rate limiting step in the myosin ATPase cycle that is catalyzed in the presence of actin?

A

ADP+Pi dissociation from myosin

M-ADP-Pi –> M + ADP + Pi

37
Q

4 steps in actin-myosin cross bridge cycle

A

M ADP Pi (hydrolyzed)
A M ADP Pi (bound)
A M (stroked)
M ATP (released)

38
Q

removing ATP halts the actin-myosin cross bridge cycle at which step?

A

rigor (prevents A-M release)

39
Q

adding ATPγS halts the actin-myosin cross bridge cycle at which step?

A

release

prevents ATP hydrolysis and A-M binding

40
Q

removing actin halts the actin-myosin cross bridge cycle at which step?

A

M-ADP-Pi (cannot bind)

41
Q

at rest, the actin-myosin cross bridge cycle is in which step?

A

M-ADP-Pi (cannot bind)

42
Q

adding AMPPNP halts the actin-myosin cross bridge cycle at which step?

A

A-M binding

AMPPNP can by hydrolyzed but not removed

43
Q

how can you prevent actin-myosin release?

A

remove ATP

44
Q

how can you prevent ATP hydrolysis by myosin?

A

ATPγS

can bind myosin but cannot be hydrolized

45
Q

how can you prevent A-M binding?

A

ATPγS

can bind myosin but cannot be hydrolized

46
Q

how can you prevent A-M power stroke?

A

AMPPNP

can be hydrolized but cannot be removed from myosin

47
Q

how can you prevent M-ADP-Pi dissociation?

A

remove (or block) actin

M-ADP-Pi dissociation occurs very slowly on its own

48
Q

how many troponin bind to one tropomyosin?

A

1

49
Q

between troponin and tropomyosin, which is globular and which is filamentous

A 
troponin = globular
tropomyosin = filamentous
50
Q

1 tropomyosin binds to how many actin monomers?

A

7

51
Q

approximately how many troponin are there per actin filament period?

A

~2
7 g-actin per tropomyosin
13-14 g-actin per period

52
Q

how many tropomyosin in a tropomyosin period?

how many actin in a tropomyosin period?

A

2 tropomyosin

14 actin

53
Q

how does a tropomyosin period compare to an actin period?

A

roughly the same but slightly larger (14 vs about 13.5 g-actin monomers)

Physiology 1 (WPH) (18 decks)

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