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MD1 Locomotor > Skeletal Muscle Function & Skeletal Muscle in Ageing and Disease > Flashcards

Skeletal Muscle Function & Skeletal Muscle in Ageing and Disease Flashcards

1
Q

Muscles with which characteristics fatigue more easily?

A

Larger, faster muscle fibres

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2
Q

Muscles with which characteristics are more fatigue resistant?

A

Smaller, slower muscle fibres

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3
Q

What are the characteristics of the vast variety of muscle fibres between fast-twitch and slow-twitch fibres?

A

Intermediate speed

Don’t fatigue as easily

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4
Q

What is muscle fibre malleability?

A

Muscles adapt to stimuli

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5
Q

What is the makeup of muscle fibres based on their type of myosin?

A

Either pure = have one type of myosin, or as hybrids containing multiple forms

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6
Q

How is lifespan/healthspan extension possible?

A

Targeting detrimental effects of ageing, including

  • Healthy lifestyle
  • Actionable/drug-treatable molecular targets
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7
Q

What does frailty and weakness confer a high risk of?

A

Mortality
Falls
Institutionalisation
Hospitalisation

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8
Q

What is sarcopenia?

A

Age-associated loss of skeletal muscle mass and function

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9
Q

What is the rate of loss of muscle mass after the age of 50?

A

1-2%

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10
Q

What is cachexia?

A

Generalised wasting of muscle and fat, typically associated with tumours

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11
Q

Are sarcopenia and cachexia the same?

A

Cachexia may be component of sarcopenia but not same thing

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12
Q

Is sarcopenia affected by health behaviours?

A

Independent of them, but good ones may slow down rate

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13
Q

In whom should sarcopenia be considered?

A

Patients who

  • Are bedridden
  • Can’t independently rise from chair
  • Have gait speed <1 m/s
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14
Q

How is sarcopenia diagnosed?

A

Gait speend of <1 m/s and appendicular lean/fat ratio is less than 2 standard deviations young adult

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15
Q

What is the effect of age on physical performance if you are a marathon runner?

A

Steady decline after peak at 20-40 years

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16
Q

What is the effect of age on physical performance if you are a weight lifter?

A

More marked decline than marathon runners

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17
Q

What is muscle weakness?

A

Inability to develop initial force appropriate for circumstances

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18
Q

When does muscle strength start to decline?

A

After age 50

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19
Q

Which muscle type shows a greater decline in strength with age?

A

Fast muscles show greater decline than slow muscles

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20
Q

What is the impact of loss of muscle strength with age?

A

Impacts progressively on physical capacity and work performance
Eventually impacts on activities often taken for granted

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21
Q

What happens if protein synthesis outweighs protein degradation in muscle?

A

Hypertrophy

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22
Q

What happens if protein degradation outweighs protein synthesis in muscle?

A

Atrophy

23
Q

What is dynapenia?

A

Age-related loss of muscle strength

24
Q

What is the association between muscle weakness and mortality?

A

Higher mortality in older people, to degree much higher than cohort who only has low lean mass

25
Q

What happens in age-related motor unit remodelling?

A

Skeletal muscle bundle innervated by type I (slow) and type II (fast) motor units in checkerboard pattern
Progressive denervation of type II motor units > fast-twitch fibres reinnervated with type I motor units > fibre becomes slow-twitch > expansion of slow motor unit

26
Q

What happens to the size and strength of muscles with age?

A

Become smaller

Strength decreases

27
Q

What happens to movement with age

A

Become slower and less precise

28
Q

What injuries do you have and increased risk of with age?

A

Falls

Fractures

29
Q

What increases as muscle mass decreases?

A

Connective tissue

Fat

30
Q

What molecular change slows muscle contractility with age?

A

Changes in Ca handling affects speed of contracction

31
Q

How do mitochondria in muscle change with age?

A

Reduced number

Loss of enzyme content

32
Q

What happens in strength training for the elderly?

A

Increases muscle strength
Increases lean total body mass
Increases muscle fibre area
Increases quality of life because of increased function

33
Q

If strength training is to be a preventative measure in sarcopenia, when must it be started?

A

Lifelong commitment > start at younger age

34
Q

What sorts of exercise can help slow the rate of age-related changes in skeletal muscle?

A

Strength training
Aerobic exercise
Flexibility
Balance

35
Q

How do hormones contribute to age-related changes in skeletal muscle?

A

Decreased circulating levels of anabolic hormones
- Growth hormone
- IGF-I
- Testosterone
Compromises efficiency of muscle regeneration as consequence of daily wear and tear

36
Q

What is muscular dystrophy?

A

Diverse group of inherited disorders characterised by progressive skeletal muscle weakness and wasting

37
Q

What causes Duchenne muscular dystrophy?

A

Lack of dystrophin

  • Complete absence/
  • Non-functional protein
38
Q

What is the inheritance pattern of Duchenne muscular dystrophy?

A

X-linked recessive

39
Q

What is the implication on genetic counselling if one in three cases of Duchenne muscular dystrophy are the result of a new mutation?

A

Even with genetic counselling, a new mutation can manifest

40
Q

What are the clinical features of Duchenne muscular dystrophy?

A

3-6 years - gait becomes lordotic and waddling
Gowers sign appears
Enlargement of calf, gluteal, lateral vastus, deltoid, and infraspinatus muscles
Muscles of lower extremity and torso more affected than upper
6-11 years - strength of limb and torso muscles decreases linearly

41
Q

What is Gowers sign?

A

Can’t stand unaided

42
Q

What does the muscle in Duchenne muscular dystrophy look like under the microscope?

A

Variation in size of muscle fibres

Infiltration by connective tissue and fat

43
Q

Are all muscles affected in Duchenne muscular dystrophy?

A

Some spared, like extraocular muscles

44
Q

What are the molecular changes to the muscle in Duchenne muscular dystrophy?

A

Small diameter of fibres
Lower mechanical stress per unit surface membrane area
Increased sarcolemmal expression of compensatory proteins

45
Q

What is the inheritance pattern of Becker muscular dystrophy?

A

X-linked recessive

46
Q

What is Becker muscular dystrophy?

A

Similar to Duchenne, but less severe
Manifests later
Slower time course

47
Q

What protein is affected in Becker muscular dystrophy?

A

Dystrophin

48
Q

What is the difference between dystrophin expression in Duchenne and Becker muscular dystrophy?

A

Duchenne - virtually no dystrophin

Becker - significant amounts of abnormal, smaller molecules

49
Q

What is dystrophin associated with in the cytoplasm?

A

Tightly associated with series of transmembrane proteins

50
Q

What does dystrophin do in muscle cells?

A

Transmits force across membrane

Stabilises sarcolemma during muscle contraction, especially lengthening actions

51
Q

What are costameres?

A

Dystrophin complexes forms rib-like lattices on cytoplasmic face of sarcolemma
Dissipates force externally

52
Q

What is the current gold standard of treatment for Duchenne muscular dystrophy?

A

Corticosteroids

53
Q

What do corticosteroids do in the treatment of Duchenne muscular dystrophy?

A

Maintain/decrease muscle fibre size
Counter effects of chronic inflammation
Preserve existing muscle fibres
Small increase in muscle strength > delays need for wheelchairs

MD1 Locomotor (17 decks)

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