Skeletal Muscle Flashcards
What are satellite cells?
Undifferentiated myogenic precursors that have self renewal properties. They are in a quiescent state, meaning they can be rapidly activated when stimulated.
Important for muscle hypertrophy and repair.
How do satellite cells work?
They become activated eg. Muscle damaging exercise,
Cells re enter cell proliferation,
Migrate to site of damage,
Cells fuse to create a myotube or to an existing g myofibre.
Outline and describe the structure of a muscle including connective tissue and components.
(Draw a flow diagram)
Muscle surrounded by epimysium -> fasicle (unit of muscle fibres) surrounded by perimysium -> muscle fibre ensheathed by endomysium (contains capillaries and nerves) ->myofibrils -> myofilaments ( actin and myosin)
Give examples of myofibril proteins
Actin, myosin, troponin, tropomyosin, titin and nebulin
Why is titin important in eccentric force production?
During eccentric contractions the myofibrils would be forcibly lengthened beyond the actin myosin overlap zone. Titin may be acting as a ‘internal spring’ able to store and release elastic potential energy, allowing the myofibrils to return to their resting length and prevent overstretching.
What’s the role of cytoskeletal proteins?
Provide structural integrity,
Allow lateral force transmission to adjacent sarcomeres,
Connect the myofibrils to cell membrane.
Outline the process of cross bridge formation
In relaxed state, the myosin head is cocked and weakly bound to actin, with tropomyosin partially blocking the A-M binding site.
Ca2+ levels increase in the cytosol and bind to troponin,
TN-Ca 2+ complex pulls tropomyosin away from the A-M binding site,
Myosin binds to actin strongly to form the cross bridge and ATP is hydrolysed causing the myosin head to cock and complete the power stroke,
ATP binds to myosin causing it to dissociate from actin,
What does the length tension relationship state?
Each sarcomere contracts with optimum force if it is at optimum length. This is due to the overlapping of actin and myosin and therefore the number of cross bridges able to form.
Why might an endurance athlete have predominantly type l muscle fibres?
They have a high resistance to fatigue, high mitochondrial density, high capillary density and a high oxidative capacity.
Why are type lla muscle fibres beneficial in lots of sports?
They have a fast contraction time high force production and high glycolysis capacity, yet also have an intermediate level of resistance to fatigue and a high level of mitochondrial density, oxidative capacity and capillary density.
What may alter your muscle phenotype?
Mechanical loading, unloading ( injury, immobility), hormones, ageing.
What are fusiform muscles? and give an example
The muscle fibres in fusiform muscles run parallel to the force-generating axis of the muscle, allowing for fast muscle shortening.
Biceps brachii
What are uni and multi pennate muscles? And give examples
Unipennate muscle fibres run at a fixed angle to the force-generating axis of the muscle, eg. Vastus lateralis. Multipennate run at several angles relative the the force generating axis, eg. Gluteus medius.
Why is a greater pennation angle beneficial in pennate muscles?
This enhances the muscles ability to pack more sarcomeres and myofibrils in the muscle fibre, thereby increasing CSA. The larger CSA increases force generating capacity of the muscle.
Why is there regional variation in strain and work within a muscle?
The curvature of the fibre, the variation in lengths and the mechanical properties of surrounding tissues result in diff muscle fibres experiencing different forces.
