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Bmsc 207 > Muscle IV > Flashcards

Muscle IV Flashcards

1
Q

What is muscle fatigue

A

Descrease in muscle tension as a result of previous contractile activity that is reversible with rest

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2
Q

What are 2 categories of muscle fatigue

A

Central and peripheral

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3
Q

What is central fatigue?

A

Feeling of tiredness and a desire to cease activity
- precedes physiological fatigue (CNS, primarily brain)
- muscles could continue

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4
Q

What influences the sensation of fatigue perceived by brain

A

Low pH from acid production during ATP hydrolysis
- H+ removed to ECF causes decline in pH

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5
Q

What is peripheral fatigue

A

Fatigue outside CNS

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6
Q

What is the theory of peripheral fatigue at the neuromuscular junction?

A
  • proposed ACh synthesis can’t keep up with neuron firing rate, decreased neurotransmitter release> decrease AChR activation on muscle> muscle fails to reach threshold for firing AP
    UNLIKELY
    Alpha motor neurons can keep up
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7
Q

What are the 3 theories about peripheral fatigue with excitation-contraction coupling?

A

Not depletion of ATP or glycogen stores
- issues with AP propagation (at t-tubule or sarcolemma)
- issues with calcium storage/uptake/release
- issues with cross bridge cycling

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8
Q

How are there issues with AP propagation

A
  • with repeated AP firing, K+ builds up in t-tubules (Extracellular space) changing threshold for APs in muscle fibre
  • generated on sarcolemma but failed down t-tubules
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9
Q

What is the peripheral fatigue theory within the muscle fibre?

A

Build up of inorganic phosphate, ADP, H+, lactate
- substances can act directly or indirectly to cause fatigue

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10
Q

What causes peripheral fatigue

A
  1. Failed excitation-contraction coupling at the t-tubule (increase in Extracellular K+)
  2. Accumulation of phosphate, acid, ADP, lactate
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11
Q

What does accumulation of phosphate, acid, ADP, lactate cause?

A
  1. Decreased in rate of Ca release, reuptake, and storage by SR
  2. Decreased activation of thin filament proteins by Ca2+
  3. Direct inhibition of binding and power stroke motion of myosin cross-bridges
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12
Q

What are the differences in skeletal muscle fibres?

A
  1. Size
  2. Colour
  3. Vascularization
  4. # mitochondria
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13
Q

What are 2 classifications of skeletal muscle

A

1, maximal velocity of shortening (fast or slow)
2. Primary pathway they use to form ATP (oxidative or glycolytic)

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14
Q

What is type I muscle fibre

A

Slow fibres containing myosin with slower ATPase activity (hydrolyze ATP slower, cross bridge slower)

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15
Q

What is type II muscle fibre

A

Fast fibres containing myosin with more rapid ATPase activity (hydrolyze ATP faster)

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16
Q

What are aerobic (oxidative) fibres?

A

Fibres containing large amount of mitochondria have high capacity for aerobic metabolism

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17
Q

What are aerobic (oxidative) fibres?

A

Fibres containing large amount of mitochondria have high capacity for aerobic metabolism
- surrounded by blood vessels and contain large amount of myoglobin to aid in oxygen delivery

18
Q

What are glycolytic fibres?

A

Fibres containing few mitochondria but an abundance of glycolytic enzymes and large store of glycogen
- look white
- only anaerobic metabolism

19
Q

What are the 3 types of skeletal muscle fibres?

A
  1. Slow oxidative (type I)
    - aerobic, small, red
  2. Fast oxidative-glycolytic fiber (Type IIa)
    - anaerobic + aerobic, medium, pink, normal functioning
  3. Fast glycolytic fiber (Type IIx)
    - fast, anaerobic, large, white
20
Q

What type of fibre creates most tension per one twitch?

A

Type IIx has large increase in tension, high fatiguability

21
Q

What fiber type is most fatiguable to least?

A

Type IIx, Type IIa, Type I

22
Q

What are the determinant of muscle force/tension development in a muscle cell?

A
  1. Fibre diameter (larger- more actin + myosin, more cross bridges)
  2. Fatiguability (amt of time fibre can develop max tension)
  3. Initial resting length
  4. Frequency of activation
23
Q

What is the amount of tension developed directly proportional to?

A

Number of cross bridges formed

24
Q

What does too much or too little overlap of thick and thin filaments in resting muscle result in?

A

Decreased tension

25
Q

What happens if sarcomeres are compressed before

A

Less force, distance to shorten is small

26
Q

What is optimal resting length?

A

Individual sarcomere has optimal overlap
- needed for adequate cycling and shortening

27
Q

What is a muscle twitch

A

Single action potential in a single muscle fibre results in an individual muscle twitch
- muscle relaxes completely between

28
Q

Is a single twitch the maximal force that a muscle fibre can develop

A

No summation of twitches can cause maximal

29
Q

How long does a single AP last for?

A

1-3ms but a muscle twitch may last up to 100ms

30
Q

What is summation

A

Subsequent AP occurs before the muscle fibre is allowed to relax a more forceful contraction occurs

31
Q

What happens during 1 AP that makes summation possible?

A
  • A single AP does not cause release of entire Ca store from SR
  • Ca from 1 AP may not activate all troponin complexes for sufficient time, some regions may be covered my tropomyosin before cycling begins
32
Q

How is summation possible?

A
  • 2nd AP causes second wave that may keep additional troponin complexes activated (more cross bridges)
  • Ca remains elevated for longer period allowing increased cross bridge cycling and further shortening of sarcomeres
33
Q

What is tetanus

A

Maintained contractile response to repeated stimuli

34
Q

What are the two forms of tetanus

A

Unfused tetanus and fused tetanus

35
Q

What is unfused tetanus

A

Reaches steady state of contraction but stimuli are far enough apart that the muscle fibre slightly relaxes between stimuli
- slight relax between twitches
- not maximal force
- approx. sustained level of tension

36
Q

What is fused tension

A

The stimulation rate is fast enough that the fibre does not relax, instead it reaches maximum tension and remains there
- looks like continuous contraction

37
Q

How much more tension is fused tetanus compared to twitch

A

2-4x more

38
Q

What is one way to increase tension developed my a single muscle fibre

A

Increase rate at which APs occur in fibre

39
Q

What is a motor unit

A

Single motor neuron and all muscle fibres it innervates, one motor neuron innervates one fibre type

40
Q

What is motor neuron pool

A

Group of all motor neurons innervating a single muscle
- in ventral horn of spinal cord

41
Q

What is motor units are recruited first when weak stimulus

A
  • weak stimulus from upper motor neuron to motor neuron pool recruits smallest motor neurons first
  • as increases, additional larger motor neurons recruited

Bmsc 207 (35 decks)

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