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Locomotor > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

What factors control muscle mass?

A

nutritional status, hormones, genetics, innervation, inflammation, oxidative stress, blood flow, exercise, disease

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2
Q

What are the different muscle fibre types

A

Type I - slow twitch and Type IIa and IIx - fast twitch

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3
Q

What is a pure muscle fibre?

A

one that contains only one type of heavy chain myosin vs hybrids which contain multiple forms

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4
Q

What are the goals of interventions for muscle wasting disorders?

A

attenuate muscle atrophy, increase muscle strength without increasing muscle fatigue

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5
Q

What is myostatin?

A

a negative regulator of muscle mass

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6
Q

What are the different types of muscle atrophy?

A

disuse atrophy, denervation atrophy, disease states e.g. cancer cachexia

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7
Q

What percentage of cancer related deaths are attributed to cachexia?

A

20%

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8
Q

What is sarcopenia?

A

age related muscle wasting associated with loss of mass and function

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9
Q

What are the causes of sarcopenia?

A

disuse, changing endocrine function, chronic diseases, inflammation, insulin resistance, nutritional deficiencies

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10
Q

How is sarcopenia diagnosed?

A

gait speed of less than 1m/s and a lean to fat ratio of less than 2 SD of the average young adult - or a loss of muscle mass combined with low muscle strength and or low physical performance

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11
Q

Can sarcopenia be stopped with healthy behaviours?

A

no

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12
Q

What is weakness?

A

an inability to develop an initial force appropriate for the circumstance

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13
Q

Are fast or slow muscles more affected by ageing?

A

fast muscles

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14
Q

What is age related motor unit remodelling?

A

denervation of type II motor units and reinnervation with type I motor units - leads to slowed contraction

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15
Q

What happens to motor neurons with age?

A

demyelination, small diameter axons, increase in connective tissue in nerves

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16
Q

What happens to the NMJ with age?

A

longer nerve terminals, fewer side branches, widening of end plate

17
Q

Can the effects of ageing on muscle be attenuated?

A

yes - through strength training before 50 years of age

18
Q

Decreased circulating levels of what hormones contribute to changes in muscle size and strength?

A

testosterone, GH, IGF-1

19
Q

What is the age of onset of duchenne muscular dystrophy?

A

2-6 years old

20
Q

What are the symptoms of duchenne muscular dystrophy?

A

generalised weakness and muscle wasting affecting limb and trunk muscles first - calves often enlarged

21
Q

What is the progression of duchenne muscular dystrophy?

A

disease progresses slowly - affects all voluntary muscles - rarely survive beyond late twenties

22
Q

What is the inheritance of duchenne muscular dystrophy?

A

X-linked recessive

23
Q

How many newborn males are affected by DMD?

A

1 in 3500-6000

24
Q

How many cases of DMD are a result of a new mutation?

A

1 in 3

25
Q

What gene is mutated in DMD?

A

dystrophin

26
Q

What is the dystrophin associated protein complex?

A

a series of transmembrane proteins associated with dystrophin which maintain the architecture of the muscle fibre as well as being involved in cell signalling

27
Q

How is dystrophin bound to the cytoskeleton?

A

via binding with F-actin

28
Q

What happens to muscles in the absence of dystrophin?

A

muscle membranes will be highly fragile and there will be decreased muscle signalling

29
Q

What is the age of onset of becker muscular dystrophy?

A

adolescence or adulthood

30
Q

What are the symptoms of becker muscular dystrophy?

A

same as DMD but less severe

31
Q

What is the progression of BMD?

A

disease progresses slowly but will affect all voluntary muscle - survive into mid to late adulthood

32
Q

What is the inheritance of BMD?

A

X-linked recessive

33
Q

What gene is affected in BMD?

A

dystrophin

34
Q

What is the difference between DMD and BMD?

A

in DMD there is a deletion in the gene which causes a frame shift so there is only synthesis of very small fragments - in BMD the reading frame is preserved so larger more useful portions of dystrophin are synthesised

35
Q

Why does a lack of dystrophin lead to degeneration of skeletal muscle?

A

a loss of dystrophin will lead to disorganised costameres, membrane leak, increased oedema, inappropriate cytosolic calcium and ROS generation and increased extracellular matrix deposition around myofibres

36
Q

What are the different ways to treat muscular dystrophy?

A

gene therapy, stem cell therapy or pharmacological intervention

37
Q

What drugs are available for muscular dystrophy?

A

corticosteroids, anabolic steroids, beta 2 agonists, IGF-1, myostatin inhibitors, proteasome inhibitors, membrane sealants, vitamin E, calcium channel blockers, heat shock protein induction

Locomotor (16 decks)

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