Skeletal muscle function, ageing and disease

Question 1

What is the most severe of all muscular dystrophies?

Answer 1

Duchene Muscular Dystrophy

Question 2

some of the factors that modulate muscle mass?

Answer 2

hormones (GH, IGF-1, testosterone)
genetics
inflammation
protein intake
protein degradation 
blood flow
exercise

Question 3

main types of fibres?

Answer 3

I —> anaerobic, slow twitching, resist exhaustion
IIa —> middle point
IIb —> aerobic, fast twitching, fast exhaustion

Question 4

what do the interventions against muscle sating requires?

Answer 4

stopping muscle atrophy
promote muscle growth
NOT –> increasing muscle fatigue

Question 5

example of genetic factors controlling muscle mass?

Answer 5

Myostatin: Negative regulator of muscle growth

Question 6

types of muscle atrophy

Answer 6

Disuse Muscle Atrophy
Denervation Atrophy
Cancer Cachexia 
Critical Illness Myopathy
Sarcopenia

Question 7

why is cancer cachexia relevant?

Answer 7

present in 80% of cases of lung, pancreas and gastrointestinal
if muscle mass 20% of cancer deaths related to this

Question 8

definition of Sarcopenia

Answer 8

age associated loss of skeletal muscle mass and function and its replacement by connective tissue and fat (also the connective tissue is more stiff)

Question 9

Diagnosis of Sarcopenia

Answer 9

• gait speed < 1m/s

* appendicular lean/fat ration of <2 SD of the average of a young adult

Question 10

people should under go a DEXA (Dual-energy X-ray absorptiometry) when

Answer 10

bedridden
cannot independently rise from a chair
gait speed < 1m/s

Question 11

Definition of weakness:

Answer 11

inability to develop an initial force appropriate for the circumstances

Question 12

at what age there is a severe drop in muscle strength? and what muscle are first affected?

Answer 12

~50

fast twitching muscles

Question 13

What is motor unit remodelling in the context of sarcopenia?

Answer 13

after loss of type 2 motor units, there is an expansion of reach of the type 1 (slow) motor units

Question 14

Sarcoplasmic reticulum dysfunction happens before any muscle loss

Answer 14

T

Question 15

in terms of the spinal cord, what are 2 changes observed with ageing?

Answer 15

loss of Type 2b fibres

reinervation (sprouting) from type 1 fibres

Question 16

some of the gradual changes seen in both pre and postsynaptic components

Answer 16

widening of the end plate
longer nerve terminals
fear side branches
loss of myelin

Question 17

changes of again in muscle are both irreversible and inevitable T/F

Answer 17

T, they can be attenuated

Question 18

Strength training in the elderly produces muscle mass recovery T/F

Answer 18

T, type 2 fibres specially increased

Question 19

Duchenne Muscular Dystrophy (DMD)
Onset?
Survival?
Inheritance

Answer 19

early childhood
rare beyond 20s (resp failure)
X-linked recessive (33% of cases new mutation)
[most common inherited childhood lethal disorder]

Question 20

in what medical condition is there pseudohypertrophy of the calf muscles?

Answer 20

Duchenne Muscular Dystrophy (DMD)

Question 21

What is the Gowers Sign?

Answer 21

climbing on one self in order to stand up from all fours (pushing on the knees)

Question 22

DMD involves a mutation on which gene?

Answer 22

mutation in the dystrophin gene (deficiency in expression due to a deletion of part of the gene and frameshift, cytoskeletal protein)

Question 23

function of dystrophin

Answer 23

structural role stabilising the cell membrane tot he laminin of the basal lamina
might have a signalling role too (anabolic role?)

Question 24

Explain the pathology of DMD

Answer 24

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

Question 25

Becker Muscular Dystrophy (BMD)
onset?
Inheritance?

Answer 25

adolescence or adulthood
X-linked recessive
same thing as Duchenne but wayyyyy less severe as there is some amounts of dystrophin still present

Question 26

reduction of force generated by muscle in relation to stretch is an indicator of….

Answer 26

Muscle Damage

Question 27

main line of treatment for DMD and BMD?

Answer 27

corticosteroids