Musculoskeletal Unit

Question 1

Name & order the connective tissue layers of muscles

Answer 1

endomysium > perimysium > epimysium

Question 2

What is the benefit of muscle fibres being multinucleated?

Answer 2

it is better for repair and growth

Question 3

What influences muscle force generation?

Answer 3

PCSA, muscle fibre pennation angle & specific tension

Question 4

True or false… the greater the pennation angle, the more force is transferred to the tendon

Answer 4

fasle, the great the angle, the less force passed through tendon

Question 5

What is specific tension? How can it help predict the force production of a muscle?

Answer 5

specific tension is the maximum force exerted by the fibres per unit of PCSA

i.e. dynamic muscles contain more fast-twitch fibres, which produce more force and fatigue quicker
postural muscles contain more slow-twitch fibres which produce less force but last longer

Question 6

How does titin contribute to muscle force & protect the sarcomere from over stretching?

Answer 6

by anchoring myosin to the z-line and by increasing in stiffness as it stretches

Question 7

What is a single motor unit?

Answer 7

a motor neurone, its axon and all the muscle fibres that it innervates

Question 8

What is Henneman’s size principle?

Answer 8

small motor units are recruited first and with greater excitatory input more units and larger units are recruited

Question 9

The maximum force that a muscle can produce depends on the contraction type. Does eccentric or concentric contraction produce more force? Why?

Answer 9

eccentric

cross-bridges hold on for longer during eccentric contraction
there is stretching of the elastic components (i.e. titin) contributing passive force to the contraction

Question 10

What are the parallel elastic components of the Hill’s mechanical model?

Answer 10

connective tissue & titin

Question 11

What are the series elastic components of the Hill’s mechanical model?

Answer 11

titin & tendon

Question 12

What are the contractile components of the Hill’s mechanical model?

Answer 12

actin & myosin cross-bridges & muscle fibres

Question 13

List 6 factors that contribute to a muscles force generation capacity

Answer 13

1. PCSA (muscle volume/fibre length)
2. specific tension
3. muscle fibre pennation angle (^ angle, less force transferred through tendon)
4. number & discharge rate of active motor units (Henneman’s size principle)
5. type and speed of contraction (eccentric vs concentric)
6. active & passive forces (passive forces more present in eccentric)

Question 14

Peripheral (muscle) fatigue may be due to what cellular level factors?

Answer 14

reduced release of acetylcholine at the neuromuscular junction
changes in the cell membrane potential/Na+/K+ pump
accumulation of metabolites which alter membrane potential (lactate/H+)
depletion of ATP/fuel

Question 15

Central (brain, spinal cord) fatigue may be due to what cellular level factors?

Answer 15

lower excitatory drive (i.e. motivation, discomfort, attention)
increased group III/IV muscle afferent input
decreased muscle spindle input increasing presynaptic inhibition

Question 16

What structures develop from the mesoderm?

Answer 16

skin, muscle & connective tissue via somites

Question 17

At what age does muscle volume typically peak?

Answer 17

25-35 years

Question 18

Define sarcopenia

Answer 18

loss of lean body mass & muscle weakness associated with aging

Question 19

Describe 7 changes in the musculotendinous unit that are likely to occur with aging

Answer 19

1. muscle fibres decrease in no. & size
2. muscle fibre type transformation (fast to slow)
3. myofilament changes (reduced elasticity)
4. reduced no. of mitochondria & loss of enzyme content (less ATP)
5. adipocyte infiltration
6. excitation-contraction coupling disruption (lack of calcium release)
7. reduced satellite cells

Question 20

Explain the typical differences in muscle size and strength observed between males and females during maturation & ageing

Answer 20

boys & girls typically develop at similar rates until 3-4 years, boys then grow quicker and at 9 years of age are at a similar height, suggesting that boys will develop more muscle mass for their height than girls

throughout the lifespan, boys are typically more active than girls which also results in greater muscle size and strength which allows this discrepancy to persist even as muscle atrophy beings after peak muscle volume (around 25-35 years)

women also experience greater muscle loss post menopause which men do not