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MSK > Muscle structure and adaptation > Flashcards

Muscle structure and adaptation Flashcards

1
Q

How do our muscles ‘get bigger’?

A
  • no increase in muscle fibre - this is genetically determined
  • growth involves increase in several fibre parameters, reflected in increased strength - increased muscle diameter
  • muscle size and function increases in proportion to body mass
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2
Q

What is isometric stress?

A

When the muscle is trying to contract but we don’t let it - measure the force that it is trying to exert

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3
Q

What is the major isoform of myosin in skeletal muscle?

A

Myosin II

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4
Q

What are the differences between the myosin isoforms?

A
  • myosin isoforms come from different genes (most part of the myosin heavy chain gene cluster on Chr17)
  • However isoform 1 is from a different chromosome altogether
  • the difference is the rate that they can hydrolyse ATP - the faster the hydrolysis, the faster the contraction will occur
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5
Q

What are the different types of myosin?

A
  • MHCemb = embryonic myosin
  • MHCIIa
  • MHCIIx/d
  • MHCIIb
  • MHCperi = perinatal myosin
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6
Q

Order the isoforms of myosin in terms of speed of ATP hydrolysis (slowest to fastest)

A

(slowest) emb, 1, 2x, 2a, 2b (fastest)
- Type 2b fibres (contain MHC2B) are fastest, gain energy fastest from electrolysis - white and are largest and strongest fibres (maximal intensity activities: 1-30 secs)
- MHC2a containing fibres are intermediate in velocity and fatigue resistant - use glycolysis and the Krebs’ cycle for enegy (high intensity activities, less than 2 mins)
- Type1 have MHC1, they are slowest contracting, gain energy anaerobically via TCA and oxphos. They are red due to high myoglobin content. Produce less power than 2b fibres but a remuch more resistant to fatigue (endurance type activities)

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7
Q

What factors will affect how a muscle fibre type will perform?

A
  • Cell lineage
  • load/stretch
  • hormones
  • motor neurones (neurotrophic substances and electrical activity)
  • will all affect speed, endurance and strength of muscle fibres
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8
Q

What is the process of muscle growth in response to intense exercise/ postnatal growth?

A
  • growth is based on damage and repair
  • process is based on stem cells (progenitors and satellite cells -> pluripotent stem cells)
  • upon injury, the satellite cells will form an asymmetric division -> myoblast maturation -> myoblast fusion
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9
Q

What is the process of muscle fibre hypertrophy?

A
  • resting myofibre (has quiescent progenitors)
  • intense exercise and microtrauma -> progenitor cell activation and proliferation (self-renewal of progenitor on fibre)
  • chemotaxis of progenitor to injure fibre
  • fusion to damaged myofibre (hypertophy)
  • OR fusion to produce new myofibres (hyperplasia)
  • regenerated myofibre with central nuclei
  • resting myofibre (nuclei migrates to edge of fibre)
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10
Q

How is Insulin-like growth factor (IGF-1) involved in growth?

A
  • IGF-1 is generated by the damaged muscle itself and stimulates its own growth (autocrine action)
  • it is also released by the liver
  • GHRH acts on the pituitary and causes GH to be released
  • acts on the liver, causing IGF-1 to be produced
  • IGF-1 then acts on muscles and bones to increase growth
  • does this by inducing the proliferation of satellite cells
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11
Q

What does normal growth and development of the limb require?

A
  • normal cell numbers
  • normal locomotor elements (e.g. bone, joint, muscles)
  • normal blood and nerve supply
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12
Q

What are motor units?

A
  • a group of muscle cells sharing one motor nerve

- one nerve contacts many muscle fibres, but one muscle fibre is supplied by only one nerve

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13
Q

What happens when you work harder?

A
  • Low intensity - only the smallest motor neurones will be firing and activating some muscles
  • motor neurones come in different sizes - depending on the strength and speed of the muscle they innervate, they vary in size
  • this is bedcause the AP will spread differently between each nerve
  • as intensity increase, the stronger muscles and larger MNs are recruited and come into play
  • the higher the recruitment, the stronger the muscle contraction will be
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14
Q

What muscle fibres are needed for: Marathon runner ?

A
  • small muscles but resistant to fatigue
  • dense muscles - strong for size
  • high oxidative capacity
  • work over very long periods
  • not explosive strength
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15
Q

What muscle fibres are needed for: Sprinter ?

A
  • adapted for explosive release of force
  • rapid powerful contractions
  • easily fatigued
  • low oxidative capacity via mitochondria
  • high force per cross sectional area of muscle
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16
Q

What muscle fibres are needed for: Powerlifter ?

A
  • adapted for immense strength
  • muscles are hypertrophied
  • highly glycolytic
  • easily fatigued
  • high muscle to body mass ratio
  • more extreme path of adaptation than sprinter
17
Q

Whats the difference between Strength and Endurance training?

A
  • S
    >high impact resistance training - maximum weights
    >increases type2 myosins and IGF-1 release
    >induces muscle fibre hypertrophy
    > increases glycolytic pathway capability
  • E
    >low impact cardio training
    >induces mitochondrial replication and increase in size and complexity
    >increased myoglobin content and so increased metabolic capability - fatigue resistance
    >induces type1 slow myosin to generate low force over long periods
18
Q

What happens when muscles get smaller?

A
  • adaptive reduction in fibre diameter

- pathological atrophy due to disuse or disease

19
Q

What happens in ageing muscles?

A
  • muscle fibres die
  • muscle atrophy
  • muscles get weaker
  • nerves remodel - lose and rearrange connections with muscles
  • muscles contract more slowly
20
Q

Are we all born with the same number of muscles?

A

YES - but may be some anatomical variation

21
Q
  • Were they all born with the same number of muscle fibres in each of their muscles?
A

YES - but may be some individual differences

22
Q

Do they all have the same genes coding for muscle proteins?

A

yes

23
Q
  • Do they all have the same versions of these genes?
A

No - polymorphisms, mutations

MSK (10 decks)

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