Skeletal Muscle Disease

Question 1

T/F Sprinters have predominantly fast twitch fibres

Answer 1

True, the muscles are large, but more prone to fatigue

Question 2

How to we intervene with muscle wasting

Answer 2

attenuate the atrophy and promote muscle strength and fatigue resistance

Question 3

Why isn’t steroid an ideal drug for muscle wasting

Answer 3

Because the increase in muscle size will just increase muscle fatigue

Question 4

How does myostatin affect muscle growth?

Answer 4

it’s a negative regulator. Muscle wasting corresponds to increase in myostatin

Question 5

What are some causes of muscle atrophy?

Answer 5

inactivity
denervation
cachexia
ageing

Question 6

How much muscle can we lose before it becomes fatal

Answer 6

40%, especially when affecting respiratory or endocrine muscles

Question 7

T/F Electrical stimulation can be used to treat muscle wasting in ICU

Answer 7

True, it turns on the physiological properties

Question 8

What is sarcopenia?

Answer 8

age-related muscle wasting and weakness

Question 9

What does an X ray image of sarcopenia patient look like?

Answer 9

the muscles are replaced by non-contractile tissue like fat and connective tissue

Question 10

How do we consider someone to have sarcopenia?

Answer 10

When patients are bedridden and cannot independently rise from a chair. Measured gait speed <1 m/s

Question 11

T/F We can prevent age-related muscle wasting

Answer 11

False, decline will still occur with best condition

Question 12

T/F Fast twitch fibres deteriorate quicker than slow twitch fibres

Answer 12

True

Question 13

What is the technical definition of “weakness”

Answer 13

inability to develop an initial force appropriate for the circumstance

Question 14

When does loss of muscle strength develop more severely

Answer 14

beyond the age of 50

Question 15

What is the neural mechanism of age related muscle remodelling

Answer 15

muscle is normally innervated by both type I and type II motor units, and with age, type II denervates first. Here, we re-innervate the loss type II units with type I units, hence remodel the muscle

Question 16

T/F Biochemical changes in muscles occur before muscle wasting

Answer 16

True, there are changes in Ca level that affect speed of contraction

Question 17

What’s the goal of treatment for patients with Duchenne Muscular Dystrophy

Answer 17

turning it into Becker Muscular Dystrophy

Question 18

T/F DMD has a late-onset

Answer 18

False, it’s early at around 2 to 6 years

Question 19

What are the symptoms of DMD?

Answer 19

generalised weakness and muscle wasting affecting limb and trunk muscles first.

Enlarged calves

Question 20

T/F DMD is a X-linked disease

Answer 20

True, X-linked recessive

Question 21

T/F DMD patients have strengthened and enlarged calves

Answer 21

False, they are hypertrophic, but it’s not muscle. It’s fats and connective tissue

Question 22

What is the Gower’s sign?

Answer 22

sign indicating weakness of proximal muscle. Patient needs to use hands to aid standing

Question 23

Which muscle is sparred in DMD?

Answer 23

extraocular muscles due to small diameter and low mechanical stress per surface area

Question 24

What’s the protein deficiency in DMD?

Answer 24

dystrophin deficiency

Question 25

What is dystrophin?

Answer 25

it’s a cytoskeletal protein that maintain the structure of muscles

actin, for example, is connected to the membrane via dystrophin

Question 26

What roles does dystrophin play aside from anchoring muscular proteins

Answer 26

signalling of muscles - anabolic signals, signal of blood flow

Question 27

how does the absence of dystrophin affect cell membrane

Answer 27

cell membrane becomes very fragile

Question 28

How is BMD different to DMD

Answer 28

BMD has later onset, slower time course, some abnormal, smaller dystrophin present. Hence, BMD is not as severe

Question 29

How does lack of dystrophin contribute to muscle wasting?

Answer 29

due to membrane instability, there may be

1) enhanced membrane leak, increased oedema and Ca
2) increased susceptibility of rupture and injury with stretch
3) inappropriate repair

Question 30

how does dystrophin affect intracellular calcium level?

Answer 30

Aside from intracellular release of Ca, there will also be Ca entry due to stretched membrane. Muscles cannot buffer the Ca, and there is increased secondary messenger activity

Question 31

What is the current treatment of muscular dystrophy

Answer 31

corticosteroids to extend the life of patients