Muscle Structure And Adaptation Flashcards
What are muscle fibres classified into?
Slow and fast twitch fibres
What type of respiration do slow twitch fibres do?
Oxidative phosphorylation
What type of respiration do fast twitch fibres do?
Glycolytic or mixed
What is the vascularisation of slow twitch fibres?
Rich
What is the vascularisation of fast twitch fibres?
Little
How many mitochondria do slow twitch fibres have?
Lots
How many mitochondria do fast twitch fibres have?
Less
How much myoglobin do slow twitch fibres have?
Lots
How much myoglobin do fast twitch fibres have?
Little
What is the max force of slow twitch fibres?
Moderate
What is the max force of fast twitch fibres?
High
Which type of twitch fibre is prone to fatigue?
Fast
What category of muscles are more likely to have a higher slow twitch proportion?
Constantly used muscles like postural muscles
What category of muscles are more likely to have a higher fast twitch proportion?
Burst of power muscles (jumping, sprinting etc)
What can vary between myofibril proteins?
Calcium sensitivity and rate of ATP hydrolysis
What are the two types of myosin isoforms?
Type I myosin heavy chain and type II heavy chain
What is the split of slow/fast twitch muscles in untrained humans?
Roughly even
What is the split of slow/fast twitch muscles in trained humans?
Increase in the fibre type they need
What does a motor unit consist of?
A motor neuron and all of the muscle fibers it innervates
How big are motor units?
Tens to many hundreds of muscle fibres
What does the size of the motor neuron correlate with?
Size of the motor unit
How can you control the level of muscle force?
Recruiting more/less muscle units
What is temporal summation?
Fusion of individual twitches to generate tetanic forces
What is the size principle?
Slow motor units are recruited first, followed by fast units for higher levels of force generation
What leads to complete muscle relaxation?
Denervation
What do we call completely relaxed muscles?
Flaccid
What drives the constant low level contractile activity of muscles?
Reflex arcs from muscle spindles
How does myogenesis work?
Paracrine factors induce myogenic regulatory factors in mesodermal precursor cells
Myoblasts proliferate under the influence of growth factors
Cell cycle exits and myogenin is expressed
Structural proteins are expressed and myotubes form from myoblasts
What is a satellite cell?
Muscle stem cells held back from differentiation to support regeneration and postnatal growth
What does muscle fibre growth involve?
Satellite cell proliferation and incorporation of nuclei into muscle fibres
What do satellite cells do when not needed?
Return to quiescence
What is hyperplasia?
Increase in muscle mass due to formation of new muscle fibres
Does hyperplasia actually happen?
Unclear - main mechanism is probably hypertrophy
What is hypertrophy?
Increase in muscle mass due to an increase in fibre size
What is sarcopenia?
Reduction in muscle mass
What is sarcopenia associated with?
Decreased satellite cell number and recruitment
What is anabolic resistance?
Reduced protein synthesis in response to hormonal stimulation or resistance exercise
