Muscle Physiology and Mechanics

Question 1

What are the stages of crossbridge cycling?

Answer 1

1) ATP binds, actin-myosin bond dissociates
2) ATP hydrolyzes, myosin head swings to next attachment site
3) ADP+Pi is released and a power-stroke occurs

Question 2

What is the state of actin-myosin when ATP is bound?

Answer 2

They are dissociated

Question 3

What is the state of actin-myosin when ATP is hydrolyzed?

Answer 3

Myosin reattaches to a new attachment site

Question 4

What is the state of actin-myosin when ADP-Pi is released?

Answer 4

Powerstroke

Question 5

What is the most important factor that modifies the number of x-bridges attached at any given time?

Answer 5

Calcium control system: more calcium = more force via more attached x-bridges

Question 6

How does filament overlap relate to the number of x-bridges attached at a given time?

Answer 6

Too much or too little overlap reduces the number of x-bridges attached

Question 7

How does speed of movement of filaments past each other relate to the number of x-bridges attached at a given time?

Answer 7

Higher speed = more likely that x-bridges will be broken and fewer x-bridges will be attached (lower force overall)

Question 8

How does speed of x-bridge cycle relate to the number of x-bridges attached at a given time?

Answer 8

Faster myosin heads = more attachments at a given filament speed

Question 9

What is force-stimulus frequency?

Answer 9

Average force increases as the number of motoneuron APs per time increases, resulting in a function that increases to a maximum force

Question 10

What is force-length property of muscle?

Answer 10

Alterations in filament overlap as a consequence of different limb positions alters the number of attached x-bridges

Question 11

What is the force-velocity principle of muscle?

Answer 11

Alteration in speed of filament movement due to speed of limb movements, numbers of attached x-bridges depend on speed of the movement vs speed of the myosin ATPase

Force decreases with shortening, but increases with lengthening

Question 12

What are three anaerobic pathways for fast movements and high forces?

Answer 12

ATP (very fast, low storage potential)
Creatine phosphate (fast, low storage potential)
Glycogen (somewhat fast, some degree of storage potential)

Question 13

What are two aerobic pathways for longer activities?

Answer 13

Glycogen (somewhat fast, some degree of storage potential)

Fat (slow, high degree of storage potential)

Question 14

What are three important properties of motor units?

Answer 14

1) contraction speed
2) fatigue resistance
3) maximum force

Question 15

What is the primary molecular mechanism of spring-like behavior in muscle?

a) attachment of calcium to troponin
b) overlap of actin and myosin filaments
c) propagation of the action potential in the muscle fiber cell membrane
d) breaking of crossbridges during movements
e) release of calcium fromthe SR

Answer 15

B) overlap of actin and myosin filaments

Question 16

The motor units in a single muscle:

a) all have the same mechanical properties
b) differ in all properties, including contraction speed, fatigue resistance, and force output
c) differ only force output, but are the same for fatigue resistance and contraction speed
d) differ only in fatigue resistance

Answer 16

b) differ in all properties, including contraction speed, fatigue resistance, and force output

Question 17

If a muscle only had spring-like behavior and no viscous-like properties, what would tend to happen when you jump down from the last step to the landing in a stair well?

a) you would bounce back up higher than where you were
b) your landing would be smooth and free of oscillations
c) you would be unable to stop yourself
d) your leg joints would be so stiff that the landing would be jarring
e) your leg joints would tend to exhibit large oscillations

Answer 17

e) your leg joints would tend to exhibit large oscillations

Question 18

During a 10s maximum speed running race, which energy substrate is the main source of ATP to support the force generated in the muscles being used?

a) glycogen via aerobic pathways
b) glycogen via anaerobic glycolysis
c) creatine phosphate (CP)
d) fat via anaerobic pathways
e) fat via aerobic pathways

Answer 18

c) creatine phosphate (CP)