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PHYS - MSS & SKIN > 4. MUSCLE STRUCTURE & ADAPTATION > Flashcards

4. MUSCLE STRUCTURE & ADAPTATION Flashcards

1
Q

What are the two types of skeletal muscle fibre?

A
  1. SLOW TWITCH MUSCLE FIBRE (Type I)

2. FAST TWITCH MUSCLE FIBRE (TYPE II)

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2
Q

What are the 7 properties of slow twitch muscle fibres?

A
  • Slow twitch muscle fibres are also known as Type I fibres. They are small diameter muscle fibres which produce slow & maintain contraction
    1. Fatigue -resistant upon repeated stimulation
    2. Oxidative metabolism
    3. Moderate peak/maximum force generated
    4. Many mitochondria
    5. Rich vasculature
    6. Small diameter
    7. High myoglobin content (O2 storing protein)
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3
Q

What are the 7 properties of fast twitch muscle fibres?

A
  • Fast twitch muscle fibres are also known as Type II muscle fibres. They are large diameter fibres which produce rapid & powerful contractions
    1. Fatigue rapidly upon repeated stimulation
    2. Have both oxidative & glycolytic capacity, capable of both
    3. High peak/moderate force generated
    4. Less mitochondria
    5. Sparse vasculature
    6. Large diameter
    7. Low myoglobin content
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4
Q

What are the metabollic differences between slow twitch & fast twitch muscle fibres?

A
  • SLOW TWITCH muscle fibres have oxidative capability. Oxidative phosphorylation occurs in the mitochondria & produces a large amount of ATP but its’ slower than glycolysis
  • ## FAST TWITCH MUSCLE FIBRES are capable of both oxidative & glycolytic metabolism. There are two types of fast twitch fibres (Type IIa & Type IIb) Glycolysis produces a smaller amount of ATP but it’s quicker than oxidative phosphorylation in the absence of oxygen
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5
Q

How do the two types of muscle fibres arise?

A
  • Th w two type of muscle fibres as a result of myosin & troponin isoforms
  • There are different myosin isoforms depending on the rate of ATP hydrolysis or shortening velocity
  • Troponin isoforms determine Ca2+ sensitivity
  • Together myosin & troponin isoforms determine fatigue resistance which is what leads to the two two muscle fibre types
  • Slow (Type 1) = fatigue resistant
  • Fast (Type II) - fatigue easily
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6
Q

What myosin heavy chains do fast & slow twitch muscle fibres express?

A
  • Slow twitch muscle fibre (Type 1) = MHCI
  • Fast twitch muscle fibre (Type 2) = MHCII
    MHC = Myosin heavy chain
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7
Q

How can muscle type affect the muscle fibre composition?

A
  • The fibre type within the muscle depends on the function of the muscle
  • Muscles have varied proportion of fast & slow twitch muscle fibres
    E.g
  • Eye muscle (lateral rectus) = fast twitch (Type I)
  • Calf (gastronemius) = Type I & II
  • Calf (soleus) = Type I
  • postural muscles which are involved in weight bearing are mainly Type I so that they don’t fatigue easily upon prolonged standing
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8
Q

How can training affect muscle fibre composition?

A
  • Activit/training can affect the proportion of muscle fibres
  • An untrained individual wiil have a 50:50 proportion of muscle fibres
  • Weight training/Sprinters = mainly fast twitch msucel (80%)
  • Long distance runners = mainly slow twitch msucle (60-70%)
  • Endurance activity = aerobic respiration, slow twitch muscle fibres
  • Anaerobic/Strength = fast twitch muscle fibres
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9
Q

What is a motor unit?

A
  • A MOTOR UNIT refers to a single motor neurones & the muscle fibres that it innervates within a target muscle
  • A target muscle can be innervated by many motor units within
  • The size of the motor neurone correlates with the size of the motor unit
  • The MOTOR POOL is all the motor neurones innervating a single muscle
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10
Q

How can we increase the force generated by a muscle in three ways?

A
  1. Increase the number of active motor units to increase the force generated - SPATIAL SUMMATION
  2. Increase the fraction/proportion of active motor units within a motor pool
  3. Increase the rate of firing by the motor unit, faster firing rate means they have less time to relax
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11
Q

What is temporal summation ?

A
  • Temporal summation refers to the total force generated from the summation of the force produced by motor units
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12
Q

What is a tetanus force & how can it be incomplete?

A
  • A tetanus force is produced when individual twitches fuse together
  • A tetanus force can be incomplete if the individual twitches don’t return to zero, so the action potential is higher each time, no time to relax
  • Incomplete tetanus force = summation of individual twitches that don’t go back down to zero
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13
Q

Describe the generation of a tetanus force in fast & slow twitch muscle fibres

A
  • FAST TWITCH MUSCLES require a higher rate of firing to generate tetanus force compared to slow twitch muscle fibres
  • SLOW TWITCH MUSCLE FIBRES are recruited first as they are smaller, followed by fast twitch muscle fibres for higher levels of force generation
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14
Q

What is myogenesis?

A

Myogenesis is the formation of skeletal muscle

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15
Q

What are the 5 steps for myogenesis?

A
  1. MYOGENIC COMMITMENT - Paracrine factors induce Myf5 & MyOD (transcription regulatory factors) in myoblasts
  2. The myoblasts proliferate due to the growth factors
  3. The myoblasts exit the cell cycle, expression of myogenin leads to terminal differentiation
  4. Structural proteins are expressed & myotubes form
  5. The myotubes allign & fuse to form multi-nucleated muscle fibres
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16
Q

What are satellite cells?

A
  • During myogenesis, a small population of myoblasts don’t form myofibres but stay close to the myofibres known as SATELLITE CELLS
  • Satellite cells are a source of new myonuclei for post-natal growth
17
Q

Describe the process of post-natal hypertrophy

A
  • Hypertrophy refers to the increase in muscle mass due the increase in muscle fibre size
  • Satellite cells act as a reservoir for undifferentiated myoblasts
  • The satellite cells proliferate, and their nuclei is incorporated into muscle fibres leading to muscle growth
  • There’s also increased protein synthesis which leads to muscle hypertrophy
18
Q

Describe the process of post-natal hyperplasia

A
  • Hyperplasia refers to an increase in muscle mass due to the formation of new muscle fibres
  • Hyperplasia leads to an increase in the number of muscle fibres, although this is genetically determined, it can change
19
Q

What’s the difference between hyperplasia & hypertrophy?

A
  • Both hypertrophy & hyperplasia lead to an increase in muscle mass
  • But hypertrophy is an increase in the size of pre-existing muscle fibres, whereas hyperplasia is the formation of new muscle fibres
20
Q

What is sarcopenia?

A
  • SARCOPENIA refers to a reduction in muscle mass
  • It’s part of the ageing process where there’s a loss of muscle fibres
  • It can also occur as result of disease or immobilisation
21
Q

What are the consequences of sarcopenia?

A
  • Sarcopenia leads to a loss of satellite cells, so there’s a loss of myonuclei. A loss of myonuclei means that hypertrophy or hyperplasia can’t occur, so no muscle growth will occur
  • Leads to anabolic resistance where there’s reduced protein synthesis in response to hormonal stimulation or resistance exercise

PHYS - MSS & SKIN (6 decks)

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