Physiology of Skeletal Muscles 2

Question 1

What does Ca bind to in the muscle fiber cytosol?

Answer 1

Troponin C

Question 2

What happens when the Ca binds to Troponin C?

Answer 2

Conformational change, and Troponin T “pulls” tropomyosin and Troponin I off of myosin-binding site of G-actin subunits

Question 3

What must happen to myosin prior to being able to bind actin?

Answer 3

Has to be energized

Question 4

When myosin is bound to ATP, it ______ its affinity for actin

Answer 4

Lowers

Question 5

What does hydrolysis of the myosin head cause?

Answer 5

Causes it to pivot and move down the actin filament

Question 6

During cross-bridge formation, the energized myosin head binds to what on actin?

Answer 6

Myosin binding site

Question 7

Most important part of cross-bridge cycle?

Answer 7

Power stroke

Question 8

During the power stroke, the Z lines get ______, shortening the sarcomere and _______.

Answer 8

Closer together; generating force

Question 9

What happens when ADP dissociates from myosin?

Answer 9

Actin-myosin complex left rigid

Question 10

What causes myosin to detach from actin?

Answer 10

ATP binding

Question 11

What happens to muscles when there is no more ATP available?

Answer 11

Muscles will contract and become rigid

Question 12

What determines the tension that is developed by a contracting muscle?

Answer 12

Amount of actin-myosin overlap

Question 13

Muscle contraction against force without decreasing the muscle length

Answer 13

Isometric contraction

Question 14

Muscle shortens against a fixed load

Answer 14

Isotonic contractions

Question 15

When the sarcolemma is no longer depolarized, what happens?

Answer 15

• L type channels back to resting state
• Calcium re-sequestered into SR

Question 16

Two main muscle fiber types?

Answer 16

• Type I - slow fibers
• Type II - fast fibers

Question 17

Type I fibers:
- Generally _______ in size
- More ________ to supply larger amounts of O2
- Lots of _________ since high levels of ox metabolism

Answer 17

• smaller
• capillaries
• mitochondria

Question 18

Type II fibers:
- _______ in size
- Lots of ___ for rapid Ca2+ release
- Lots of _____ enzymes

Answer 18

• Larger
• SR
• glycolytic

Question 19

Two categories of Type II (fast) fibers

Answer 19

• Type IIA - fast oxidative glycolytic fibers
• Type IIB - fast glycolytic fibers

Question 20

3 metabolic systems responsible for continuous supply of ATP to muscle fibers?

Answer 20

1. Phosphagen system
2. Glycogen-lactic acid system
3. Aerobic system

Question 21

T/F: High energy phosphate bond of ATP has more energy than the bond of phosphocreatine

Answer 21

FALSE

Question 22

Phosphocreatine Serves as a rapidly mobilizable reserve of high energy phosphates in what?

Answer 22

Skeletal muscle and brain

Question 23

How long does phosphagen system provide maximal power?

Answer 23

8-10 seconds

Question 24

What is pyruvate converted to with insufficient oxygen?

Answer 24

Lactic acid

Question 25

What enzyme converts pyruvate -> lactic acid?

Answer 25

Lactate dehydrogenase

Question 26

How long does glycogen-lactic acid system provide maximal power?

Answer 26

60-90 seconds

Question 27

What is the OVERALL net loss or gain of ATP in the Cori cycle?

Answer 27

4 ATP lost

Question 28

What is the purpose of the Cori cycle?

Answer 28

Providing muscles with 2 ATP, replenishing NAD+ = prevents buildup of lactic acid since it lowers pH, causes cramping

Question 29

As long as nutrients in the body last, the aerobic system can be used for how long?

Answer 29

Unlimited duration

Question 30

What system can replenish ATP, phosphocreatine, and glycogen-lactic acid system?

Answer 30

Oxidative metabolism

Question 31

What is “oxygen debt”?

Answer 31

After exercise is over, stored oxygen must be replenished - usually need to take in 11.5 L

Question 32

What is the main determinant of muscle strength?

Answer 32

Size

Question 33

What is the maximum contractile force for a muscle?

Answer 33

3-4 kg/cm2

Question 34

How do you measure muscle power?

Answer 34

Amount of work that the muscle can perform in a given time

Question 35

What does muscle endurance depend on?

Answer 35

Nutritive support = amount of glycogen that has been stored

Question 36

If muscles function under no load, what are the results?

Answer 36

They will increase little in strength

Question 37

What will cause approximate optimal increase in muscle strength?

Answer 37

6 nearly maximal muscle contractions in 3 sets for 3 days/week

Question 38

What results from an increase in the number of actin and myosin filaments in each muscle fiber = enlarges individual muscle fibers?

Answer 38

Muscle hypertrophy

Question 39

What is the rare formation of new muscle fibers called?

Answer 39

Muscle hyperplasia

Question 40

How does hyperplasia happen?

Answer 40

Occurs due to linear splitting of previously enlarged fibers

Question 41

What causes new sarcomeres to be added at the ends of the muscle fibers where they attach to the tendons?

Answer 41

Muscle lengthening

Question 42

What happens when muscle no longer receives contractile signals required to maintain normal muscle size

Answer 42

Muscle atrophy

Question 43

What causes muscle atrophy?

Answer 43

• Denervation/neuropathy
• Tenotomy
• Sedentary lifestyle
• Plaster cast
• Space flight (micro-gravity)

Question 44

What happens in acute/subacute atrophy?

Answer 44

• degenerate contractile proteins
• decrease max force
• decrease velocity of contraction

Question 45

What happens in chronic atrophy?

Answer 45

• Number of sarcomeres lost = shortening of muscle
• Fiber replaced by fibrous and fatty tissue