Skeletal muscle Flashcards
What is the epimysium?
Ensheathment of entire muscle
What is the perimysium?
Ensheathment of muscle fibres into bundles
What is the endomysium?
Areolar connective tissue that ensheaths each individual myocyte (separating muscle fibres). It also contains capillaries and nerves
What are the three stages of myogenesis?
Determination
Myoblast proliferation/migration
Muscle differentiation
What are the first signs of muscle commitment?
Appearance of AChRs all over sarcolemma
Formation of actin and myosin filaments, no sarcomeres
what is myosin?
actin-dependent ATPase
What is oxidative capacity?
Microlitres of oxygen consumed per gram of muscle per hour
- depends on capillary density, oxygen carrying capacity of blood (rbc count), myoglobin presence, amount of oxygen utilised (number of mitochondria present)
What are 3 pathways for ATP regeneration?
1) direct phosphorylation of creatine kinase
2) anaerobic glycolysis
3) oxidative phosphorylation in mitochondria
what is CrP level at rest?
~30mM
What is EPOC?
excess post-exercise oxygen consumption
-> allows restoration of CrP, glycogen
What are the 4 main tasks to complete post exercise?
Replenishment of ATP and phosphocreatine
Removal (oxidation) of lactic acid
Replenishment of myoglobin with oxygen
Replenishment of glycogen
What is the structure of myosin?
Hexamer
2 identical heavy chains, 2 essential light chains, 2 regulatory light chains
globular head, 2 alpha helices forming super helical rod
What are three theories of muscle fatigue?
1) Conduction Failure - due to the build-up of external K+ within T-tubules –> Action Potential (AP) failure
2) Lactic acid build-up associated with anaerobic glycolysis: when the rate of lactate production exceeds the rate of its disappearance –> acidification –> conformational changes in muscle proteins
3) Inhibition of X-bridge cycling due to the build-up of ADP and Pi
Are muscle fibres of the same type located together?
A motor unit/all muscle fibres innervated by one motoneuron are of the same type
All muscles contain a mixture of fibre types
How is tension varied in muscle?
orderly recruitment of motor neurons
The small motor units are most excitable and are recruited first. They develop low forces that can be maintained for long periods. The large motor units
are recruited later, after ~ 40% of the maximal tension in a whole muscle had been reached
What are the effects of endurance training?
augmentation of oxidative mechanisms
increase in capillary density, more mitochondria
What are the effects of strength training?
larger pale FG fibres
What are the three stages of myogenesis?
myoblast determination
myoblast proliferation, migration
differentiation
Which muscle types have high oxidative capacity?
Slow Oxidative Red (I) and Fast-Oxidative Glycolytic (IIA and IID)
Which muscle types have high myosin ATPase activity?
Fast Oxidative glycolytic red (IIA, IID) and fast glycolytic white (IIB)
What are the steps of muscle contraction?
1) muscle AP propagated
2) Ca released from lateral sac
3) Ca binds troponin, removes blocking action of tropomyosin
4) cross bridge moves
5) Ca taken up
6) Ca removal from troponin –> muscle relaxes
Which process leads to lactic acid build up?
glycolysis
How can fatty acids be utilised to produce ATP?
oxidative phosphorylation
