Skeletal Muscle Ageing and Disease

Question 1

What are the criteria for diagnosis of sarcopenia?

Answer 1

A gait speed of <1m/s

Appendicular lean/fat ratio of <2SD of the average young adult

Question 1

What type of muscle is more affected by ageing?

Answer 1

Fast twitch

Question 1

What changes occur at the motorneuron level with age?

Answer 1

Increase in the amount of connective tissue

Aberrant, small diameter axons

Dysmyelination

Question 2

What is Gower’s sign?

Answer 2

Stepping forwards along the floor into a standing position

Question 4

What are the goals of therapy to attenuate muscle wasting?

Answer 4

Attenuate muscle atropy

Promote muscle strength

Question 5

What is the name of the most severe muscular dystrophy?

Answer 5

Duchenne muscular dystrophy

Question 5

Which muscles are preferentially affected in DMD?

Answer 5

Limb and trunk muscles

Question 6

What happens to neuromuscular plate with age?

Answer 6

Widened end plate

Fewer side branches

Longer nerve terminals

Question 6

What is the best intervention for sarcopenia?

Answer 6

Strength training to converse strength and attenuate wasting

Question 7

When does DMD present?

Answer 7

At 2-6 years old

Question 9

Do muscles usually have only one type of muscle fibre that best suits their function, eg the soleus only has slow twitch fibres

Answer 9

No, muscles generally have a mixture of fibres even if they have specific functions

Question 10

What is the inheritance pattern of Duchenne muscular dystrophy?

Answer 10

X-linked recessive

Question 10

What treatment is currently used for muscular dystrophy?

Answer 10

Glucocorticosteroids

Question 11

What are the causes of sarcopenia?

Answer 11

Disuse

Endocrine changes

Chronic diseases

Inflammation

Insulin resistance

Nutrient deficiencies

Question 12

Which protein is deficient in DMD?

Answer 12

Dystrophin

Question 12

What is the difference between DMD and Becker muscular dystrophy in terms of clinical course?

Answer 12

Becker muscular dystrophy has a later onset, and slower progression

Question 14

What replaces muscle lost with ageing?

Answer 14

Fat and connective tissue

Question 16

Describe age related muscle remodelling

Answer 16

Fast twitch fibres become deinnervated

Some are lost

Others are reinnervated by slow twitch motor neurons

Overall there is a decrease in mass and proportionate increase in slow twitch fibres

Question 17

How does the lack of dystrophin effect cell physiology?

Answer 17

Increases its susceptibility to injury

• Makes the cell membrane leaky > Ca influx > Hypercontractility and necrosis

Question 18

How do DMD patients eventually die?

Answer 18

Cardiorespiratory failure

Question 19

What is the pathogenesis cycle of the muscular dystrophy?

Answer 19

Increase cellular damage followed repair but eventually the rate of damage overtakes the ability to repair

Question 21

What causes slower contraction and reduced force of contraction of muscles that occurs before loss of muscle mass?

Answer 21

Slowed release and uptake of Ca

Question 22

At what age does muscle strength decline occur more rapidly?

Answer 22

>50 years old

Question 24

Apart from loss of muscle mass, what also occurs in cachexic muscles?

Answer 24

Loss of muscle architecture

Question 25

What is the postulated role of dystrophin protein?

Answer 25

It provides structure support to stabilize the sarcolemma (myocyte cell membrane) during muscle contraction

Question 26

What the average survival time of DMD?

Answer 26

Late twenties

Question 27

What contributes to accelerated muscular atropy in ICU patients?

Answer 27

The inflammatory state

Question 28

What effect does myostatin have on muscle mass?

Answer 28

Causes a decrease in mass

Question 29

Which anabolic hormones decline with ageing?

Answer 29

GH

IGF-1

Testosterone

Question 30

How much muscle must be lost during cachexia for death to occur?

Answer 30

>40%