Muscle Contraction

Question 1

What are the functions of muscle? (4)

Answer 1

Convert chemical energy to mechanical energy

Movement (and act as a brake)

Hold structures in body together

Heat source

Question 2

How much lean body mass is muscle?

Answer 2

75%

Question 3

What is the composition of muscle?

Answer 3

75% water

20% protein

5% inorganic salts and other

Question 4

What percentage of actin and myosin make up the total protein in muscle?

Answer 4

20% actin

40% myosin

Question 5

Describe the structure of a muscle

Answer 5

Myofibres packed with myofibrils

Endomysium surrounds individual myofibres

Myofibres arranged into fascicles surrounded by perimysium

Bundles of fascicles wrapped in epimysium

Question 6

How are muscles attached to bone?

Answer 6

Tendons

Question 7

What are the four steps of the cross-bridge cycle?

Answer 7

1. Attachment: myosin head binds with actin at exposed binding site
2. Release: ATP binds to myosin head causing myosin to detach from actin
3. Bending: ATP hydrolysis provides energy for myosin head to rotate (5nm towards plus end)
4. Force generation: myosin head binds to actin (further along), ADP + Pi released, power stroke to original head position

Question 8

What causes the exposure of the actin binding sites?

Answer 8

Calcium ions binding to troponin on tropomyosin causes actin conformational change

Question 9

What is a twitch?

Answer 9

Mechanical response to a single electrical impulse

Question 10

What is the time between the impulse and a twitch called?

Answer 10

Electromechanical delay

Question 11

What does TPT mean?

Answer 11

Time to peak tension

Question 12

What does Pt mean?

Answer 12

Peak tension

Question 13

What is 1/2 RT?

Answer 13

Half relaxation time

Question 14

What is a tetanus?

Answer 14

Mechanical response to multiple stimuli

Question 15

How long does the half removal of calcium ions take after stimulation?

Answer 15

80ms

Question 16

Why do you get a fused tetanus when the frequency of stimulation increases?

Answer 16

Insufficient time to remove calcium ions

Or

Calcium ion concentration builds up

Question 17

Why is a high frequency/rate of impulses beneficial in sustained contraction?

Answer 17

Consistently high calcium ion concentrations

Cross-bridge cycling can continue uninterrupted

Question 18

What is the muscle fibre type determined by?

Answer 18

Myosin heavy chain isoform composition

Question 19

Are type I muscle fibres fast or slow twitch?

Answer 19

Slow

Question 20

Are type II muscle fibres fast or slow twitch?

Answer 20

Fast

Question 21

How long do type I muscle fibres take to reach peak isometric force?

Answer 21

110ms

Question 22

How long do type II muscle fibres take to reach peak isometric force?

Answer 22

50ms

Question 23

What is the most fatigue-resistant muscle fibre type?

Answer 23

Type I

Question 24

Which type II muscle fibre type is more fatigue-resistant?

Answer 24

IIa

Question 25

What is the effect of type I fibres reaching tetanus at lower stimulation frequencies?

Answer 25

Reach maximal force at lower levels of stimulation

Question 26

What is a motor unit?

Answer 26

A single motor neuron and all the muscle fibres it innervates

Question 27

What are the two types of motor unit recruitment?

Answer 27

Spatial Temporal

Question 28

What is spatial recruitment?

Answer 28

Recruiting minimum number of motor units Recruit smallest motor units first

Question 29

Why are small motor units able to be recruited first in spatial recruitment?

Answer 29

Lower stimulus threshold than large motor units

Question 30

What is temporal recruitment?

Answer 30

Motor units can discharge action potentials at higher frequencies to generate greater force

Question 31

What does rate coding refer to?

Answer 31

Motor unit firing rate

Question 32

What type of muscles are masticatory muscles?

Answer 32

Pennate

Question 33

What bone are the masticatory muscles attached to?

Answer 33

Mandible

Question 34

Describe the motor units of the masseter

Answer 34

Small number of motor units Highly variable in size and fibre type composition

Question 35

What does the masseter muscle being heterogenous mean?

Answer 35

Has both fast and slow twitch fibres