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BMS03 > Muscle Contraction > Flashcards

Muscle Contraction Flashcards

1
Q

What are the functions of muscle? (4)

A

Convert chemical energy to mechanical energy

Movement (and act as a brake)

Hold structures in body together

Heat source

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2
Q

How much lean body mass is muscle?

A

75%

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3
Q

What is the composition of muscle?

A

75% water

20% protein

5% inorganic salts and other

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4
Q

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

A

20% actin

40% myosin

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5
Q

Describe the structure of a muscle

A

Myofibres packed with myofibrils

Endomysium surrounds individual myofibres

Myofibres arranged into fascicles surrounded by perimysium

Bundles of fascicles wrapped in epimysium

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6
Q

How are muscles attached to bone?

A

Tendons

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7
Q

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

A
  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
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8
Q

What causes the exposure of the actin binding sites?

A

Calcium ions binding to troponin on tropomyosin causes actin conformational change

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9
Q

What is a twitch?

A

Mechanical response to a single electrical impulse

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10
Q

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

A

Electromechanical delay

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11
Q

What does TPT mean?

A

Time to peak tension

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12
Q

What does Pt mean?

A

Peak tension

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13
Q

What is 1/2 RT?

A

Half relaxation time

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14
Q

What is a tetanus?

A

Mechanical response to multiple stimuli

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15
Q

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

A

80ms

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16
Q

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

A

Insufficient time to remove calcium ions

Or

Calcium ion concentration builds up

17
Q

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

A

Consistently high calcium ion concentrations

Cross-bridge cycling can continue uninterrupted

18
Q

What is the muscle fibre type determined by?

A

Myosin heavy chain isoform composition

19
Q

Are type I muscle fibres fast or slow twitch?

A

Slow

20
Q

Are type II muscle fibres fast or slow twitch?

A

Fast

21
Q

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

A

110ms

22
Q

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

A

50ms

23
Q

What is the most fatigue-resistant muscle fibre type?

A

Type I

24
Q

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

A

IIa

25
Q

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

A

Reach maximal force at lower levels of stimulation

26
Q

What is a motor unit?

A

A single motor neuron and all the muscle fibres it innervates

27
Q

What are the two types of motor unit recruitment?

A

Spatial

Temporal

28
Q

What is spatial recruitment?

A

Recruiting minimum number of motor units

Recruit smallest motor units first

29
Q

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

A

Lower stimulus threshold than large motor units

30
Q

What is temporal recruitment?

A

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

31
Q

What does rate coding refer to?

A

Motor unit firing rate

32
Q

What type of muscles are masticatory muscles?

A

Pennate

33
Q

What bone are the masticatory muscles attached to?

A

Mandible

34
Q

Describe the motor units of the masseter

A

Small number of motor units

Highly variable in size and fibre type composition

35
Q

What does the masseter muscle being heterogenous mean?

A

Has both fast and slow twitch fibres

BMS03 (12 decks)

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