Quiz 4

Question 1

What is the end-plate potential?

Answer 1

Occurs at motor end plate of sarcolemma (muscle cell) that always causes AP.

Question 2

Each muscle action potential generates a _____ _______.

Answer 2

Single twitch

Question 3

What is excitation -contraction coupling?

Answer 3

The sequence of muscle action potentials and Ca2+ release that initiates contraction

Question 4

What are t-tubules? What do they do?

Answer 4

Inward extensions of sarcolemma that propagated sarcolemmal action potentials.

Question 5

What is the sarcoplasmic reticulum?

Answer 5

Similar to endoplasmic reticulum, sequesters Ca2+ in a muscle cell.

Question 6

What happens after an action potential has propagated a long a t-tubule?

Answer 6

The action potential activated DHP receptor that mechanically opens the ryanodine receptor in the sarcoplasmic reticulum to release Ca2+.

Question 7

What is the contraction cycle?

Answer 7

Ca2+ binds to troponin –> moves tropomyosin –> exposes entire binding site on actin –> sliding filaments allow muscle to shorten

Question 8

What are the steps of the contraction cycle?

Answer 8

1. Myosin in resting “cocked” state
2. Power stroke activated by Ca2+
3. Enters rigor state
4. Myosin releases actin

Question 9

What happens when myosin is in the “cocked” phase?

Answer 9

-Bound to ADP and Phosphate
-Weakly bound to actin

Question 10

What happens in the power stroke phase?

Answer 10

-Myosin bound strongly to actin
-Phosphate released
-Myosin head swivels toward M line

Question 11

What happens in the Rigor state?

Answer 11

-Myosin releases ADP
-Myosin strongly bound to actin (stuck until another ATP can come & release myosin)

Question 12

What causes Myosin to release actin?

Answer 12

ATP binds to myosin

Question 13

What moves Myosin back to the “cocked” position?

Answer 13

ATP hydrolysis

Question 14

What terminates the contraction cycle?

Answer 14

Calcium pumped back into SR by Ca2+ ATPase

Question 15

What are the types of skeletal muscle fibers?

Answer 15

1. Type 1 (slow oxidative)
2. Type 2a (fast oxidative-glycolytic)
3. Type 2b/x (Fast glycolytic)

Question 16

What are the characteristics of Type 1 skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:

Answer 16

Speed: Slowest
Myosin ATPase activity: slow
Diameter: small
Endurance: fatigue resistance

Question 17

What are the characteristics of Type 1 skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:

Answer 17

Metabolism: Aerobic (uses O2)
Capillary Density: High
Mitochondria: Many
Myoglobin content: High

Question 18

What are the characteristics of Type 2a skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:

Answer 18

Speed: Intermediate
Myosin ATPase activity: Fast
Diameter: Medium
Endurance: Fatigue Resistence

Question 19

What are the characteristics of Type 2b/x skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:

Answer 19

Speed: Fastest
Myosin ATPase activity: Fast
Diameter: Large
Endurance: Easily fatigued

Question 20

What are the characteristics of Type 2a skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:

Answer 20

Metabolism: Intermediate
Capillary Density: Medium
Mitochondria: Moderate
Myoglobin content: Moderate

Question 21

What are the characteristics of Type 2b/x skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:

Answer 21

Metabolism: Anaerobic (uses glycolysis & fermentation)
Capillary Density: Low
Mitochondria: Few
Myoglobin content: Low

Question 22

What type of muscle fibers mostly make up postural muscles?

Answer 22

Type 1

Question 23

What type of muscle fibers mostly make up short bursts?

Answer 23

Type 2

Question 24

What are the factors influencing force production?

Answer 24

-Fiber length
-Summation
-Motor Units

Question 25

How does summation increase force?

Answer 25

Increased stimulus frequency causes insufficient time to pump Ca2+ back into SR between twitches. The continuing contraction allows more force to be produced.

Question 26

What is tetanus?

Answer 26

State of maximal contraction

Question 27

What is unfused tetanus?

Answer 27

Relaxes slightly between stimuli

Question 28

What is fused tetanus?

Answer 28

Sustained maximal tension

Question 29

What is a motor unit?

Answer 29

Somatic motor neuron and all the muscle fibers it innervates.

Question 30

What are the characteristics of motor units?

Answer 30

-all muscle fibers in motor units are same type & twitch together
-each muscle fiber only innervated by 1 motor unit

Question 31

A muscle unit with few fibers produces what kind of movement?

Answer 31

Fine movements, slow twitch

Question 32

A muscle unit with 1000s of fibers produces what kind of movement?

Answer 32

Big movements, fast twitch

Question 33

How do muscles vary force?

Answer 33

-Motor unit recruitment
-Frequency coding

Question 34

Which muscles are recruited first and why?

Answer 34

Small, slow-twitch muscle units are recruited first while large, fast twitch units are held in reserve because you can wait until you need a lot of force since they are easily fatigued.

Question 35

How does frequency coding vary muscle force?

Answer 35

Increase in AP frequency leads to summation which increase the muscle force.

Question 36

What is hypertrophy?

Answer 36

Resistance exercise can lead to muscle fibers thickening & getting bigger

Question 37

What is atrophy?

Answer 37

Disuse of muscles can lead to the muscle fibers getting thinner & shrinking