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BMS1052 > 16 - Controlling Contractions > Flashcards

16 - Controlling Contractions Flashcards

1
Q

What are the 2 aspects to delay in axon conduction velocity?

A
  • conduction/latency

- delay in NMJ

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2
Q

Conduction/latency

A

Time taken for AP to travel from point of stimulation to NMJ

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3
Q

Delay in NMJ

A

Process by which ACh vesicles fuse w/ membrane, release and bind to post-synaptic receptors

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4
Q

What’s the motor end plate?

A

Post-synaptic region of NMJ

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5
Q

Why is Ca2+ only briefly available in the intracellular space of muscle cell?

A

When Ca2+ floods out of SR, it’s simultaneously being actively pumped back into SR by Ca2+-ATPase

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6
Q

What has to be available for cross-bridge cycling to occur?

A

Ca2+ and ATP

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7
Q

When does cross-bridge cycling stop?

A

When all Ca2+ pumped back into SR

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8
Q

What does Ca2+ limit?

A

Duration of cross-bridge cycling

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9
Q

What does ATP limit?

A

How quickly cross-bridge cycling occurs (more ATP = faster)

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10
Q

Sliding filament theory

A

Myosin heads marching along actin, pulling Z discs towards centre of sarcomere

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11
Q

Latent period

A

Before force generation

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12
Q

Contraction period

A

Force always increasing and Ca2+ binding to troponin, revealing actin binding sites

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13
Q

Relaxation period

A

All Ca2+ pumped back into SR

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14
Q

What are 2 reasons for latent period?

A
  • takes time for AP to be conducted to muscle

- additional latent period after release of ACh reflects Ca2+ release from SR

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15
Q

What limits maximum force generation?

A
  • takes time for cross-bridge binding to occur

- passive muscle tension

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16
Q

If 2nd stimulation occurs during contraction period…

A

Force will smoothly summate but if arrives during relaxation period, unfused tetanus occurs

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17
Q

Titin filaments

A

3rd protein filament integrated into sarcomeres

Somewhat elastic and accounts for passive muscle tension

18
Q

Optimal length

A

Dependent on optimal overlap of actin and myosin

19
Q

Maximum length

A

No overlap of actin and myosin

20
Q

Minimum length limited by

A

Thin filament overlap

overlap of this filaments and Z discs

21
Q

Isotonic contractions

A

Muscle changes length while maintaining constant tension

22
Q

Isometric contractions

A

Muscle develops tension without changing length

23
Q

Time-course of force generation in isometric contraction

A
  • force generation begins from time of first cross-bridge attachment
  • total duration depends on sequestration of Ca2+ by SR
24
Q

Time-course of force generation in isotonic contraction

A
  • evidence of shortening delayed until enough cross-bridges have attached to counteract load
  • shortening ends once load returns to resting position
25
Q

Concentric muscle contraction

A

Bicep muscle shortening while contracting

26
Q

Eccentric muscle contraction

A

Bicep muscle lengthening while contracting

27
Q

Concentric

A

After power stroke, myosin head progressively binds further along actin, leading to shortening

28
Q

Eccentric

A

External force applied to muscle means it lengthens even as power strokes occur

29
Q

How are types of skeletal muscle fibre defined?

A
  1. Max shortening velocity

2. ATP pathway

30
Q

Max shortening velocity

A

Type 1 - slow; low ATPase activity

Type 2 - fast; high ATPase activity

31
Q

What does ATPase activity affect?

A

Max rate of cross bridge cycling

32
Q

ATP pathway

A

A) oxidative - depend on oxygen (numerous mitochondria, good blood supply, lots of myoglobin, red)

B) glycolysis - large glycogen stores(thicker, greater tension development, white)

33
Q

What are the 3 fibre types?

A

1a - slow oxidative
2a - fast oxidative
2b - fast glycolytic

34
Q

T/F muscle fibres in single muscle unit are different types

A

False - same type

35
Q

If experimentally change type of AP stimulation, can change type of…

A

Muscle fibre that it appears to be

36
Q

Type 1 fibres have motor units that

A

Have smaller cell bodies and smaller diameter axons

Produce steady, low freq activity

37
Q

Type II fibres have motor units that

A

Have larger cell bodies and larger diameter axons

Produce occasional high freq bursts

38
Q

T/F small units are recruited last

A

False - recruited first

39
Q

Forcing slow motor neurons to innervate fast-twitch muscles causes a change in…

A

Muscle fibre phenotype

40
Q

What have chronic low freq stimulation experiments shown?

A

Pattern and type of APs coming in to a fibre determine fibre’s type

BMS1052 (10 decks)

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