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CFoM > 05b: Muscle Mechanics > Flashcards

05b: Muscle Mechanics Flashcards

1
Q

When muscle first assembles, the first two myosin molecules interact in which orientation? How are subsequent myosin molecules bound?

A

Tail-to-tail; all subsequent molecules bind to preceding ones in head-to-tail fashion

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2
Q

The striated muscle’s (X) filaments are bipolar.

A

X = thick

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3
Q

Myosin heads have binding sites for:

A

Actin and ATP

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4
Q

T/F: Mechanism of contraction differs slightly among various muscle types.

A

False - mechanism is the same in all

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5
Q

T/F: Different isoforms of myosin found in different muscle types.

A

True

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6
Q

Slow-twich skeletal muscle has a contraction velocity similar to that of (X) muscle.

A

X = cardiac

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7
Q

On/off switching of which muscle types is thin-filament based? Elaborate.

A

Skeletal muscle and cardiac muscle; based on troponin/tropomyosin

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8
Q

On/off switching of which muscle types is thick-filament based? Elaborate.

A

Smooth muscle; based on myosin phosphorylation

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9
Q

Describe the orientation of actin/myosin in rigor state.

A

Myosin bound to actin at an angle and cannot be released, since there’s no ATP to bind the myosin heads

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10
Q

Describe the orientation of actin/myosin in relaxed state.

A

Myosin at 90 degrees, not bound to actin; ATP is hydrolyzed, but lack of Ca means binding sites on actin not exposed

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11
Q

The “power stroke” occurs as soon as:

A

ADP and Pi are dissociated from the myosin head

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12
Q

One troponin molecule is linked to (X) tropomyosin molecule(s), which extend(s) over (Y) actin monomers.

A 
X = one
Y = 7
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13
Q

What are the components of troponin?

A
  1. Troponin T
  2. Troponin I
  3. Troponin C
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14
Q

Troponin T function

A

Links troponin/tropomyosin complex

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15
Q

Troponin I function

A

Inhibits myosin-actin interaction

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16
Q

Troponin C function

A

Relieves Troponin I inhibition, upon binding Ca

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17
Q

If only Troponin (X) and (Y) existed, the muscle would be constitutively off.

A 
X = T
Y = I
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18
Q

In an isometric contraction, what general change(s) occur in muscle?

A

Force develops, but no shortening occurs

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19
Q

Give example of isometric contraction.

A

Pushing against a wall

20
Q

In isotonic contraction, what general change(s) occur in muscle?

A

Muscle shortens

21
Q

In isotonic contraction, tension in muscle is (less than/greater than) weight of load.

A

Equal to

22
Q

Passive tension, aka (X), demonstrates which property of the tissue?

A

X = preload

Elastic property

23
Q

(X) is primarily responsible for the muscle’s preload?

A

X = Titin

24
Q

Length of time of the mechanical event (contraction) depends on:

A

How quickly calcium is re-sequestered (aka the SR ATPase activity)

25
Q

Compare the Ca levels released in a single twitch vs in tetanus.

A

Identical

26
Q

For simplicity, all elasticity of muscle can be attributed to:

A

the thin filaments

27
Q

Total muscle tension equals:

A

Active Tension + Passive tension

28
Q

Define “rest length”

A

The muscle length at which max active tension can be produced

29
Q

An muscle holding a 300g load: how much tension is present in the series elastic component?

A

None! SEC only responds to active tension

30
Q

An muscle holding a 300g load: where is the tension (i.e. what’s supporting this load)?

A

Titin

31
Q

An muscle holding a 300g load: what’s the preload and after load?

A

Preload: 300g

No after load without active tension

32
Q

Increasing the load will have which effect(s) on the process of lifting that load?

A
  1. Increase latent period (time between stimulus and external shortening)
  2. Decrease extent of shortening
  3. Decrease velocity of shortening
33
Q

Myosin in smooth muscle is in (X) polar arrangement.

A

X = side

34
Q

In smooth muscle, actin is bound to:

A

Dense plaques and bodies

35
Q

Which steps in actomyosin ATPase cycle are (slower/faster) in smooth muscle than in skeletal/cardiac muscle?

A

Slower; all steps are slower

36
Q

T/F: Smooth muscle splits less ATP than other muscle types, making its cycle more economical.

A

True

37
Q

Ca source in smooth muscle:

A
  1. Extracellular

2. Internal stores

38
Q

In smooth muscle, describe series of events that occur upon Ca presence in cell.

A
  1. Binds calmodulin
  2. Ca-calmodulin bind/activate myosin light chain kinase
  3. Kinase phosphorylates myosin light chain
  4. Myosin can interact with actin
39
Q

List some examples of molecules that can regulate smooth muscle contraction.

A
  1. cAMP levels
  2. Rho kinase
  3. cGMP levels
40
Q

How can epinephrine/NE affect smooth muscle contraction?

A
  1. Bind beta receptors, increase cAMP
  2. cAMP activates PKA
  3. PKA induces Ca re-sequestering
  4. Smooth muscle relaxes
41
Q

How can adrenaline affect smooth muscle contraction?

A
  1. Activates Rho kinase
  2. Rho kinase phosphorylates the phosphorylase (inactivates it)
  3. Increased activation of smooth muscle
42
Q

How can NO affect smooth muscle contraction?

A
  1. High concentration increases cGMP concentration
  2. Activation of Protein Kinase G, which inhibits Rho Kinase
  3. Increase in phosphatase activity
  4. Smooth muscle relaxes
43
Q

Viagra mechanism of action.

A

Inhibits breakdown of cGMP

44
Q

Smooth muscle’s ability to maintain tone over long period of time is due to special (Ca/myosin/ATP) levels.

A

Due to special latch mechanism

45
Q

T/F: Smooth muscle latch mechanism is identical to rigor state in skeletal muscle.

A

False - similar state, but occurs in presence of ATP

46
Q

Stretch-activated channels on smooth muscle allow which specific ion in?

A

Fairly nonspecific - allow Na, K, Ca, Mg

47
Q

There are (few/many) stretch-activated channels on smooth muscle membrane. Their activation causes (X), which then affects (Y).

A

Few;
X = local depolarization
Y = nearby channels

CFoM (18 decks)

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