05b: Muscle Mechanics Flashcards
When muscle first assembles, the first two myosin molecules interact in which orientation? How are subsequent myosin molecules bound?
Tail-to-tail; all subsequent molecules bind to preceding ones in head-to-tail fashion
The striated muscle’s (X) filaments are bipolar.
X = thick
Myosin heads have binding sites for:
Actin and ATP
T/F: Mechanism of contraction differs slightly among various muscle types.
False - mechanism is the same in all
T/F: Different isoforms of myosin found in different muscle types.
True
Slow-twich skeletal muscle has a contraction velocity similar to that of (X) muscle.
X = cardiac
On/off switching of which muscle types is thin-filament based? Elaborate.
Skeletal muscle and cardiac muscle; based on troponin/tropomyosin
On/off switching of which muscle types is thick-filament based? Elaborate.
Smooth muscle; based on myosin phosphorylation
Describe the orientation of actin/myosin in rigor state.
Myosin bound to actin at an angle and cannot be released, since there’s no ATP to bind the myosin heads
Describe the orientation of actin/myosin in relaxed state.
Myosin at 90 degrees, not bound to actin; ATP is hydrolyzed, but lack of Ca means binding sites on actin not exposed
The “power stroke” occurs as soon as:
ADP and Pi are dissociated from the myosin head
One troponin molecule is linked to (X) tropomyosin molecule(s), which extend(s) over (Y) actin monomers.
X = one Y = 7
What are the components of troponin?
- Troponin T
- Troponin I
- Troponin C
Troponin T function
Links troponin/tropomyosin complex
Troponin I function
Inhibits myosin-actin interaction
Troponin C function
Relieves Troponin I inhibition, upon binding Ca
If only Troponin (X) and (Y) existed, the muscle would be constitutively off.
X = T Y = I
In an isometric contraction, what general change(s) occur in muscle?
Force develops, but no shortening occurs
Give example of isometric contraction.
Pushing against a wall
In isotonic contraction, what general change(s) occur in muscle?
Muscle shortens
In isotonic contraction, tension in muscle is (less than/greater than) weight of load.
Equal to
Passive tension, aka (X), demonstrates which property of the tissue?
X = preload
Elastic property
(X) is primarily responsible for the muscle’s preload?
X = Titin
Length of time of the mechanical event (contraction) depends on:
How quickly calcium is re-sequestered (aka the SR ATPase activity)
Compare the Ca levels released in a single twitch vs in tetanus.
Identical
For simplicity, all elasticity of muscle can be attributed to:
the thin filaments
Total muscle tension equals:
Active Tension + Passive tension
Define “rest length”
The muscle length at which max active tension can be produced
An muscle holding a 300g load: how much tension is present in the series elastic component?
None! SEC only responds to active tension
An muscle holding a 300g load: where is the tension (i.e. what’s supporting this load)?
Titin
An muscle holding a 300g load: what’s the preload and after load?
Preload: 300g
No after load without active tension
Increasing the load will have which effect(s) on the process of lifting that load?
- Increase latent period (time between stimulus and external shortening)
- Decrease extent of shortening
- Decrease velocity of shortening
Myosin in smooth muscle is in (X) polar arrangement.
X = side
In smooth muscle, actin is bound to:
Dense plaques and bodies
Which steps in actomyosin ATPase cycle are (slower/faster) in smooth muscle than in skeletal/cardiac muscle?
Slower; all steps are slower
T/F: Smooth muscle splits less ATP than other muscle types, making its cycle more economical.
True
Ca source in smooth muscle:
- Extracellular
2. Internal stores
In smooth muscle, describe series of events that occur upon Ca presence in cell.
- Binds calmodulin
- Ca-calmodulin bind/activate myosin light chain kinase
- Kinase phosphorylates myosin light chain
- Myosin can interact with actin
List some examples of molecules that can regulate smooth muscle contraction.
- cAMP levels
- Rho kinase
- cGMP levels
How can epinephrine/NE affect smooth muscle contraction?
- Bind beta receptors, increase cAMP
- cAMP activates PKA
- PKA induces Ca re-sequestering
- Smooth muscle relaxes
How can adrenaline affect smooth muscle contraction?
- Activates Rho kinase
- Rho kinase phosphorylates the phosphorylase (inactivates it)
- Increased activation of smooth muscle
How can NO affect smooth muscle contraction?
- High concentration increases cGMP concentration
- Activation of Protein Kinase G, which inhibits Rho Kinase
- Increase in phosphatase activity
- Smooth muscle relaxes
Viagra mechanism of action.
Inhibits breakdown of cGMP
Smooth muscle’s ability to maintain tone over long period of time is due to special (Ca/myosin/ATP) levels.
Due to special latch mechanism
T/F: Smooth muscle latch mechanism is identical to rigor state in skeletal muscle.
False - similar state, but occurs in presence of ATP
Stretch-activated channels on smooth muscle allow which specific ion in?
Fairly nonspecific - allow Na, K, Ca, Mg
There are (few/many) stretch-activated channels on smooth muscle membrane. Their activation causes (X), which then affects (Y).
Few;
X = local depolarization
Y = nearby channels
