Muscle Contraction Flashcards
What are the functions of muscle? (4)
Convert chemical energy to mechanical energy
Movement (and act as a brake)
Hold structures in body together
Heat source
How much lean body mass is muscle?
75%
What is the composition of muscle?
75% water
20% protein
5% inorganic salts and other
What percentage of actin and myosin make up the total protein in muscle?
20% actin
40% myosin
Describe the structure of a muscle
Myofibres packed with myofibrils
Endomysium surrounds individual myofibres
Myofibres arranged into fascicles surrounded by perimysium
Bundles of fascicles wrapped in epimysium
How are muscles attached to bone?
Tendons
What are the four steps of the cross-bridge cycle?
- Attachment: myosin head binds with actin at exposed binding site
- Release: ATP binds to myosin head causing myosin to detach from actin
- Bending: ATP hydrolysis provides energy for myosin head to rotate (5nm towards plus end)
- Force generation: myosin head binds to actin (further along), ADP + Pi released, power stroke to original head position
What causes the exposure of the actin binding sites?
Calcium ions binding to troponin on tropomyosin causes actin conformational change
What is a twitch?
Mechanical response to a single electrical impulse
What is the time between the impulse and a twitch called?
Electromechanical delay
What does TPT mean?
Time to peak tension
What does Pt mean?
Peak tension
What is 1/2 RT?
Half relaxation time
What is a tetanus?
Mechanical response to multiple stimuli
How long does the half removal of calcium ions take after stimulation?
80ms
Why do you get a fused tetanus when the frequency of stimulation increases?
Insufficient time to remove calcium ions
Or
Calcium ion concentration builds up
Why is a high frequency/rate of impulses beneficial in sustained contraction?
Consistently high calcium ion concentrations
Cross-bridge cycling can continue uninterrupted
What is the muscle fibre type determined by?
Myosin heavy chain isoform composition
Are type I muscle fibres fast or slow twitch?
Slow
Are type II muscle fibres fast or slow twitch?
Fast
How long do type I muscle fibres take to reach peak isometric force?
110ms
How long do type II muscle fibres take to reach peak isometric force?
50ms
What is the most fatigue-resistant muscle fibre type?
Type I
Which type II muscle fibre type is more fatigue-resistant?
IIa
What is the effect of type I fibres reaching tetanus at lower stimulation frequencies?
Reach maximal force at lower levels of stimulation
What is a motor unit?
A single motor neuron and all the muscle fibres it innervates
What are the two types of motor unit recruitment?
Spatial
Temporal
What is spatial recruitment?
Recruiting minimum number of motor units
Recruit smallest motor units first
Why are small motor units able to be recruited first in spatial recruitment?
Lower stimulus threshold than large motor units
What is temporal recruitment?
Motor units can discharge action potentials at higher frequencies to generate greater force
What does rate coding refer to?
Motor unit firing rate
What type of muscles are masticatory muscles?
Pennate
What bone are the masticatory muscles attached to?
Mandible
Describe the motor units of the masseter
Small number of motor units
Highly variable in size and fibre type composition
What does the masseter muscle being heterogenous mean?
Has both fast and slow twitch fibres
