Skeletal Muscle Disease Flashcards
T/F Sprinters have predominantly fast twitch fibres
True, the muscles are large, but more prone to fatigue
How to we intervene with muscle wasting
attenuate the atrophy and promote muscle strength and fatigue resistance
Why isn’t steroid an ideal drug for muscle wasting
Because the increase in muscle size will just increase muscle fatigue
How does myostatin affect muscle growth?
it’s a negative regulator. Muscle wasting corresponds to increase in myostatin
What are some causes of muscle atrophy?
inactivity
denervation
cachexia
ageing
How much muscle can we lose before it becomes fatal
40%, especially when affecting respiratory or endocrine muscles
T/F Electrical stimulation can be used to treat muscle wasting in ICU
True, it turns on the physiological properties
What is sarcopenia?
age-related muscle wasting and weakness
What does an X ray image of sarcopenia patient look like?
the muscles are replaced by non-contractile tissue like fat and connective tissue
How do we consider someone to have sarcopenia?
When patients are bedridden and cannot independently rise from a chair. Measured gait speed <1 m/s
T/F We can prevent age-related muscle wasting
False, decline will still occur with best condition
T/F Fast twitch fibres deteriorate quicker than slow twitch fibres
True
What is the technical definition of “weakness”
inability to develop an initial force appropriate for the circumstance
When does loss of muscle strength develop more severely
beyond the age of 50
What is the neural mechanism of age related muscle remodelling
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
T/F Biochemical changes in muscles occur before muscle wasting
True, there are changes in Ca level that affect speed of contraction
What’s the goal of treatment for patients with Duchenne Muscular Dystrophy
turning it into Becker Muscular Dystrophy
T/F DMD has a late-onset
False, it’s early at around 2 to 6 years
What are the symptoms of DMD?
generalised weakness and muscle wasting affecting limb and trunk muscles first.
Enlarged calves
T/F DMD is a X-linked disease
True, X-linked recessive
T/F DMD patients have strengthened and enlarged calves
False, they are hypertrophic, but it’s not muscle. It’s fats and connective tissue
What is the Gower’s sign?
sign indicating weakness of proximal muscle. Patient needs to use hands to aid standing
Which muscle is sparred in DMD?
extraocular muscles due to small diameter and low mechanical stress per surface area
What’s the protein deficiency in DMD?
dystrophin deficiency
What is dystrophin?
it’s a cytoskeletal protein that maintain the structure of muscles
actin, for example, is connected to the membrane via dystrophin
What roles does dystrophin play aside from anchoring muscular proteins
signalling of muscles - anabolic signals, signal of blood flow
how does the absence of dystrophin affect cell membrane
cell membrane becomes very fragile
How is BMD different to DMD
BMD has later onset, slower time course, some abnormal, smaller dystrophin present. Hence, BMD is not as severe
How does lack of dystrophin contribute to muscle wasting?
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
how does dystrophin affect intracellular calcium level?
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
What is the current treatment of muscular dystrophy
corticosteroids to extend the life of patients
