Musculoskeletal Unit Flashcards
Name & order the connective tissue layers of muscles
endomysium > perimysium > epimysium
What is the benefit of muscle fibres being multinucleated?
it is better for repair and growth
What influences muscle force generation?
PCSA, muscle fibre pennation angle & specific tension
True or false… the greater the pennation angle, the more force is transferred to the tendon
fasle, the great the angle, the less force passed through tendon
What is specific tension? How can it help predict the force production of a muscle?
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
How does titin contribute to muscle force & protect the sarcomere from over stretching?
by anchoring myosin to the z-line and by increasing in stiffness as it stretches
What is a single motor unit?
a motor neurone, its axon and all the muscle fibres that it innervates
What is Henneman’s size principle?
small motor units are recruited first and with greater excitatory input more units and larger units are recruited
The maximum force that a muscle can produce depends on the contraction type. Does eccentric or concentric contraction produce more force? Why?
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
What are the parallel elastic components of the Hill’s mechanical model?
connective tissue & titin
What are the series elastic components of the Hill’s mechanical model?
titin & tendon
What are the contractile components of the Hill’s mechanical model?
actin & myosin cross-bridges & muscle fibres
List 6 factors that contribute to a muscles force generation capacity
- PCSA (muscle volume/fibre length)
- specific tension
- muscle fibre pennation angle (^ angle, less force transferred through tendon)
- number & discharge rate of active motor units (Henneman’s size principle)
- type and speed of contraction (eccentric vs concentric)
- active & passive forces (passive forces more present in eccentric)
Peripheral (muscle) fatigue may be due to what cellular level factors?
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
Central (brain, spinal cord) fatigue may be due to what cellular level factors?
lower excitatory drive (i.e. motivation, discomfort, attention)
increased group III/IV muscle afferent input
decreased muscle spindle input increasing presynaptic inhibition
What structures develop from the mesoderm?
skin, muscle & connective tissue via somites
At what age does muscle volume typically peak?
25-35 years
Define sarcopenia
loss of lean body mass & muscle weakness associated with aging
Describe 7 changes in the musculotendinous unit that are likely to occur with aging
- muscle fibres decrease in no. & size
- muscle fibre type transformation (fast to slow)
- myofilament changes (reduced elasticity)
- reduced no. of mitochondria & loss of enzyme content (less ATP)
- adipocyte infiltration
- excitation-contraction coupling disruption (lack of calcium release)
- reduced satellite cells
Explain the typical differences in muscle size and strength observed between males and females during maturation & ageing
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
