Skeletal muscle function, ageing and disease Flashcards
What is the most severe of all muscular dystrophies?
Duchene Muscular Dystrophy
some of the factors that modulate muscle mass?
hormones (GH, IGF-1, testosterone) genetics inflammation protein intake protein degradation blood flow exercise
main types of fibres?
I —> anaerobic, slow twitching, resist exhaustion
IIa —> middle point
IIb —> aerobic, fast twitching, fast exhaustion
what do the interventions against muscle sating requires?
stopping muscle atrophy
promote muscle growth
NOT –> increasing muscle fatigue
example of genetic factors controlling muscle mass?
Myostatin: Negative regulator of muscle growth
types of muscle atrophy
Disuse Muscle Atrophy Denervation Atrophy Cancer Cachexia Critical Illness Myopathy Sarcopenia
why is cancer cachexia relevant?
present in 80% of cases of lung, pancreas and gastrointestinal
if muscle mass 20% of cancer deaths related to this
definition of Sarcopenia
age associated loss of skeletal muscle mass and function and its replacement by connective tissue and fat (also the connective tissue is more stiff)
Diagnosis of Sarcopenia
- gait speed < 1m/s
* appendicular lean/fat ration of <2 SD of the average of a young adult
people should under go a DEXA (Dual-energy X-ray absorptiometry) when
bedridden
cannot independently rise from a chair
gait speed < 1m/s
Definition of weakness:
inability to develop an initial force appropriate for the circumstances
at what age there is a severe drop in muscle strength? and what muscle are first affected?
~50
fast twitching muscles
What is motor unit remodelling in the context of sarcopenia?
after loss of type 2 motor units, there is an expansion of reach of the type 1 (slow) motor units
Sarcoplasmic reticulum dysfunction happens before any muscle loss
T
in terms of the spinal cord, what are 2 changes observed with ageing?
loss of Type 2b fibres
reinervation (sprouting) from type 1 fibres
some of the gradual changes seen in both pre and postsynaptic components
widening of the end plate
longer nerve terminals
fear side branches
loss of myelin
changes of again in muscle are both irreversible and inevitable T/F
T, they can be attenuated
Strength training in the elderly produces muscle mass recovery T/F
T, type 2 fibres specially increased
Duchenne Muscular Dystrophy (DMD)
Onset?
Survival?
Inheritance
early childhood
rare beyond 20s (resp failure)
X-linked recessive (33% of cases new mutation)
[most common inherited childhood lethal disorder]
in what medical condition is there pseudohypertrophy of the calf muscles?
Duchenne Muscular Dystrophy (DMD)
What is the Gowers Sign?
climbing on one self in order to stand up from all fours (pushing on the knees)
DMD involves a mutation on which gene?
mutation in the dystrophin gene (deficiency in expression due to a deletion of part of the gene and frameshift, cytoskeletal protein)
function of dystrophin
structural role stabilising the cell membrane tot he laminin of the basal lamina
might have a signalling role too (anabolic role?)
Explain the pathology of DMD
loss of dystrophin molecule in the cell membrane that helps anchor it to the basal lamina causes rupture of the membrane upon forceful contraction allowing for the influx of Ca+2 and increased production of ROS, necrosis and oedema
