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SGUL - Physiology 2 > Muscle Structure & Adaptation > Flashcards

Muscle Structure & Adaptation Flashcards

1
Q

State the 2 different types of groups that skeletal muscles can be classified into

A
  • Slow twitch fibres (Type I)
  • Fast twitch fibres (Type II)
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2
Q

Outline the features of the Slow twitch fibres (Type I)

A
  • Fatigue resistant
  • Moderate max force
  • Oxidative
  • Many mitochondria
  • Rich vascularisation
  • Small diameter
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3
Q

Outline the features of the Fast twitch fibres (Type II)

A
  • Fatigue rapidly
  • High max force
  • Glycolytic (IIx) or mixed (IIa)
  • Fewer mitochondria
  • Sparser vascularisation
  • Larger diameter
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4
Q

State the visible features that allows you to differentiate between slow twitch and fast twitch fibres

A
  • Slow twitch fibres have high myoglobin which appears as red muscle
  • Fast twitch fibres have low myoglobin which appear as white muscle
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5
Q

What are the structural and metabolic differences between the 2 groups?

A
  • When slow twitch fibres are stained for capillaries, the microscope shows a small cross sectional diameter muscle surrounded by more capillaries
  • When fast Twitch fibres are stained for oxidative enzymes, the microscope shows a darker staining which shows higher capacity for oxidative metabolism
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6
Q

What do myofibril proteins exist as?

A

As multiple isoforms with different functional characteristics

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7
Q

Describe one form of these myofibrils

A
  • Vertebrate sarcomere structure essentially the same
  • But functional tuning occurs via isoforms of muscle proteins
  • Variable Ca sensitivity (troponin, tropomyosin)
  • Slow twitch fibres (type I) express type I myosin heavy chain
  • Fast twitch fibres (Type II) express type II MHC
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8
Q

What does the fibres type do when it is present in a muscle?

A

Fibres type composition of muscles adapts to function
- Muscle vary in proportion of type I / type II fibres
- Lateral rectus (eye muscle) mainly type II fast twitch
- Gastrocnemius (calf muscle) mixed type I & II
- Soleus (Calf) more type I slow twitch

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9
Q

What are the listed effects of training specific fibres types?

A
  • Long and middle runners: 60-70% have slow twitch fibres
  • Sprinters: 80% have fast twitch fibres
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10
Q

Summarise what Slow twitch fibres (Type I) are

A
  • Slow maintained contraction, fatigue resistant
  • is Oxidative, has lots of mitochondria and vascularisation, myoglobin
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11
Q

Summarise what Fast twitch fibres (Type I) are

A
  • Rapid powerful contractions that fatigue easily
  • Glycolytic or moderate oxidative capacity, few mitochondria, lack myoglobin and poor vascularisation
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12
Q

Briefly summarise how myofibril proteins exist and the composition of muscle fibre types

A
  • Myofibril proteins exist as multiple isoforms with different functional character
  • Muscle fibre type composition be different in different muscles
  • Muscle fibre types can adapt over time to the needs of the body
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13
Q

How is force generation in a muscle controlled?

A

Controlled at the level of the mortar unit

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14
Q

Describe the function and structure of the mortar unit

A
  • The mortar unit consists of a mortar neuron and the set of muscle fibres within a muscle that it innervates
  • Motor unit size ranges from 10 to many 100s of muscle fibres
  • A muscle may be innervated by 10s to 100s of mortar MNs
  • The size of the MN correlates with the size of the motor unit
  • Muscle fibres of a motor unit are generally of the same type
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15
Q

What is a temporal summation in a muscle fibre?

A
  • Fusion of individual twitches generates tetanus forces
  • VD to describe graph
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16
Q

Compare and contrast the fast and slow motor units

A
  • Fast motor units (A) need higher firing rates to generate tetanic forces than slow motor units
  • Slow motor units are recruited first, followed by fast units followed by higher levels of force generation
17
Q

What happens to the skeletal muscle tone when at rest?

A
  • Most muscles at rest exhibit some low level of contractile activity
  • Denervarion leads to complete relaxation (flaccid)
  • Driven by reflex arcs from muscle spindles (sectioning dorsal roots abolishes resting tone)
18
Q

Describe the process of myogenesis? (Part 1)

A
  • Paracrine factors induce myogenic regulatory factors (MRFs) in the mesodermal precursor cells (myogenic commitment myoblasts
  • Myoblast proliferate under influence of growth factors
  • Cell cycle exit, myogenin expression – terminal differentiation
19
Q

Describe the process of myogenesis? (Part 2)

A
  • Structural proteins expressed and myotubes form from myoblasts
  • Myotubes align and fuse, becoming multinucleated muscle fibres
  • Satellite cells: regeneration and postnatal
20
Q

Describe how postnatal muscle growth: hypertrophy occurs (Part 1)

A
  • After birth, increase in muscle mass due to increase in fibre size (hypertrophy)
  • Muscle Stem Cells called satellite cells. Undifferentiated muscle precursors, self renewing
  • Muscle fibre growth involves satellite cell proliferation and incorporation of nuclei into muscle fibres. Increased protein synthesis and muscle fibre size (hypertrophy)
21
Q

Describe how postnatal muscle growth: hypertrophy occurs (Part 2)

A
  • Muscle fibre growth involves satellite cell proliferation and incorporation of nuclei into muscle fibres. Increased protein synthesis and muscle fibre size (hypertrophy)
  • Muscle fibres are multinucleated. Maintain cytoplasm: nuclei ratio
  • Satellite cells return to quiescence when not
22
Q

Describe how Postnatal muscle growth: Hyperplasia occurs

A
  • Increase in muscle mass due to formation of new muscle fibres
  • Some evidence from animal models
  • Uncertain whether this happens – main mechanism is probably hypertrophy
23
Q

Describe the fundamentals of the ageing muscle: sarcopenia

A
  • Sarcopenia: reduction in muscle mass
  • Part of ageing process
  • Atrophy of muscle fibres
  • May be due to disease or immobilisation
  • Associated with decreased satellite cell number and recruitment
  • Anabolic resistance – reduced protein synthesis in response to hormonal stimulation or resistance exercise
  • Can be resisted

SGUL - Physiology 2 (37 decks)

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