L10.2 Plasticity 1

Question 1

Possible fibres combinations in mucsles?

Answer 1

• Fibres can be pure or contain multiple forms
• Up to 4x types in small, only 3x in humans

Question 2

MyHC

Answer 2

• MyHC (proteins of type 2 fibres) isoforms differ in functional properties
• Influenced by hormone levels, exercise injury & aging

Question 3

MyLC

Answer 3

• MyLC: Modulate actin-myosin interactions
• Stabilise head, influence speed of contraction

Question 4

Transition & transformation of fibre types?

Answer 4

• Transition of fibre types is plausible, but transformation is hard through training
• Metabolic enz, capillaries, t-system → easier to change than contractile proteins

Question 5

/What happens after cross-reinnervation of muscle fibres?

Answer 5

• Cross over nerve inputs: Slow receive fast input, vice versa
• Muscle changed colour → biochemical properties changed
• Conclude: Nerve input → dictates properties of muscles (contracility & fatigue resistance)
  
  • Freq → determines fibre type
  • Total # of impulses → determines fatiguability of fibres

Question 6

S.A.I.D principle?

Answer 6

• S.A.I.D principle (specific adaptation to imposed demands):
• Properties of muscles altered depending on muscle stimuli

Question 7

What happens during inactivity of muscles?

Answer 7

• Atrophy of muscles:
  
  • 40% loss of thigh vol in 6 weeks
  • Shrinkage of existing fibres (slow fibres affected first in humans)
  • If immobilised in lengthened position → allows better persevation of mass & function

Question 8

What is muscle plasticity?

Answer 8

• Transformation of muscle fibre types
  
  • Transformation plausible as muscle is being rearranged as it is still physiologically active
• Changes metabolic & contractile properties (Not from the loss of one type and regeneration with another)
  
  • ↑capillary deensity
  • Proliferation of mitochondria (↑oxidative state → becomes redder)
  • ↓SR & Ca2+ ATPase (However, SR swells in the first few hours)
• Transformation takes a long time (Continuous stimulation)
  
  • ∴ very hard with exercise

Question 9

What happens after chronic stimulation of muscle?

Answer 9

• Changes in fatiguability but no change in myosin isoform expressions
• Sequence of adaptation:
  
  • Ca2+ → enz activites → MyHC changes
• After 14 days:
  
  • Z-bands ↑ width & ↓ activity → not necessarily = ↑muscle proteins
  • ↓density of T-system

Question 10

Adaptations to physical activities

Answer 10

• Adaptations from training easily & rapidly reversible
  
  • ↑oxidative enzyme activities during endurance training takes months
  • Fast decline within a few weeks after stopping of training
• Muscle mass ↓ after transformation (from fast → slow), but not necesarrily viewed as degenerative/atrophic
  
  • Electrical stimulation makes muscles smaller

Question 11

Differences b/w voluntary exercise & electrical stimulation

Answer 11

• Voluntary exercise: Only part of muscle is used, some fibres recruited
• Electrical stimulation: All fibres recruited