05b: Muscle Mechanics

Question 1

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

Answer 1

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

Question 2

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

Answer 2

X = thick

Question 3

Myosin heads have binding sites for:

Answer 3

Actin and ATP

Question 4

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

Answer 4

False - mechanism is the same in all

Question 5

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

Answer 5

True

Question 6

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

Answer 6

X = cardiac

Question 7

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

Answer 7

Skeletal muscle and cardiac muscle; based on troponin/tropomyosin

Question 8

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

Answer 8

Smooth muscle; based on myosin phosphorylation

Question 9

Describe the orientation of actin/myosin in rigor state.

Answer 9

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

Question 10

Describe the orientation of actin/myosin in relaxed state.

Answer 10

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

Question 11

The “power stroke” occurs as soon as:

Answer 11

ADP and Pi are dissociated from the myosin head

Question 12

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

Answer 12

X = one
Y = 7

Question 13

What are the components of troponin?

Answer 13

1. Troponin T
2. Troponin I
3. Troponin C

Question 14

Troponin T function

Answer 14

Links troponin/tropomyosin complex

Question 15

Troponin I function

Answer 15

Inhibits myosin-actin interaction

Question 16

Troponin C function

Answer 16

Relieves Troponin I inhibition, upon binding Ca

Question 17

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

Answer 17

X = T
Y = I

Question 18

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

Answer 18

Force develops, but no shortening occurs

Question 19

Give example of isometric contraction.

Answer 19

Pushing against a wall

Question 20

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

Answer 20

Muscle shortens

Question 21

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

Answer 21

Equal to

Question 22

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

Answer 22

X = preload

Elastic property

Question 23

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

Answer 23

X = Titin

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Identical

Question 26

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

Answer 26

the thin filaments

Question 27

Total muscle tension equals:

Answer 27

Active Tension + Passive tension

Question 28

Define "rest length"

Answer 28

The muscle length at which max active tension can be produced

Question 29

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

Answer 29

None! SEC only responds to active tension

Question 30

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

Answer 30

Titin

Question 31

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

Answer 31

Preload: 300g | No after load without active tension

Question 32

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

Answer 32

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

Question 33

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

Answer 33

X = side

Question 34

In smooth muscle, actin is bound to:

Answer 34

Dense plaques and bodies

Question 35

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

Answer 35

Slower; all steps are slower

Question 36

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

Answer 36

True

Question 37

Ca source in smooth muscle:

Answer 37

1. Extracellular | 2. Internal stores

Question 38

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

Answer 38

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

Question 39

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

Answer 39

1. cAMP levels 2. Rho kinase 3. cGMP levels

Question 40

How can epinephrine/NE affect smooth muscle contraction?

Answer 40

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

Question 41

How can adrenaline affect smooth muscle contraction?

Answer 41

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

Question 42

How can NO affect smooth muscle contraction?

Answer 42

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

Question 43

Viagra mechanism of action.

Answer 43

Inhibits breakdown of cGMP

Question 44

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

Answer 44

Due to special latch mechanism

Question 45

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

Answer 45

False - similar state, but occurs in presence of ATP

Question 46

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

Answer 46

Fairly nonspecific - allow Na, K, Ca, Mg

Question 47

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

Answer 47

Few; X = local depolarization Y = nearby channels