Skeletal Muscle Ageing and Disease Flashcards
What are the criteria for diagnosis of sarcopenia?
A gait speed of <1m/s
Appendicular lean/fat ratio of <2SD of the average young adult
What type of muscle is more affected by ageing?
Fast twitch
What changes occur at the motorneuron level with age?
Increase in the amount of connective tissue
Aberrant, small diameter axons
Dysmyelination
What is Gower’s sign?
Stepping forwards along the floor into a standing position
What are the goals of therapy to attenuate muscle wasting?
Attenuate muscle atropy
Promote muscle strength
What is the name of the most severe muscular dystrophy?
Duchenne muscular dystrophy
Which muscles are preferentially affected in DMD?
Limb and trunk muscles
What happens to neuromuscular plate with age?
Widened end plate
Fewer side branches
Longer nerve terminals
What is the best intervention for sarcopenia?
Strength training to converse strength and attenuate wasting
When does DMD present?
At 2-6 years old
Do muscles usually have only one type of muscle fibre that best suits their function, eg the soleus only has slow twitch fibres
No, muscles generally have a mixture of fibres even if they have specific functions
What is the inheritance pattern of Duchenne muscular dystrophy?
X-linked recessive
What treatment is currently used for muscular dystrophy?
Glucocorticosteroids
What are the causes of sarcopenia?
Disuse
Endocrine changes
Chronic diseases
Inflammation
Insulin resistance
Nutrient deficiencies
Which protein is deficient in DMD?
Dystrophin
What is the difference between DMD and Becker muscular dystrophy in terms of clinical course?
Becker muscular dystrophy has a later onset, and slower progression
What replaces muscle lost with ageing?
Fat and connective tissue
Describe age related muscle remodelling
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
How does the lack of dystrophin effect cell physiology?
Increases its susceptibility to injury
- Makes the cell membrane leaky > Ca influx > Hypercontractility and necrosis
How do DMD patients eventually die?
Cardiorespiratory failure
What is the pathogenesis cycle of the muscular dystrophy?
Increase cellular damage followed repair but eventually the rate of damage overtakes the ability to repair
What causes slower contraction and reduced force of contraction of muscles that occurs before loss of muscle mass?
Slowed release and uptake of Ca
At what age does muscle strength decline occur more rapidly?
>50 years old
Apart from loss of muscle mass, what also occurs in cachexic muscles?
Loss of muscle architecture
What is the postulated role of dystrophin protein?
It provides structure support to stabilize the sarcolemma (myocyte cell membrane) during muscle contraction
What the average survival time of DMD?
Late twenties
What contributes to accelerated muscular atropy in ICU patients?
The inflammatory state
What effect does myostatin have on muscle mass?
Causes a decrease in mass
Which anabolic hormones decline with ageing?
GH
IGF-1
Testosterone
How much muscle must be lost during cachexia for death to occur?
>40%
