Skeletal Muscle Flashcards
What is each muscle myofibril divided into?
Sarcomere
What is the sarcomere?
The contractile unit of skeletal muscle
What are the proteins in the sarcomere?
Actin
Myosin
Titin
What is the role of the T-Tubules?
Allows rapid spread of the muscle action potential
What are essential for muscle contraction?
ATP and calcium
What are the components of the thin filament?
Troponin
Tropomyosin
Globular actin
What are the properties of slow twitch/red/type I muscle fibers?
Postural muscles
Myoglobin
Mitochondria
Oxidative metabolism
Fatigue resistant
What are the properties of fast twitch/white/type II muscle fibers?
Less myoglobin
Less mitochondria
Fatigue prone
Glycolytic metabolism
Define a motor unit.
A somatic motor neurone and all the muscle fibers innervated by that neurone
Where do alpha motor neurones originate?
Ventral horn of the spinal cord
What does the muscle action potential do?
Triggers release of Ca++ from the SR through the ryanodine receptor
What does the muscle action potential do?
Triggers release of Ca++ from the SR through the ryanodine receptor
What does Ca++ bind to on the thin filament?
Troponin C
What happens when actin-myosin interaction cause?
Sarcomere shortens
What is muscle relaxation associated with?
Ca++ pumped back into SR
Where are DHPR receptors found?
Embedded in the T-tubules
What is DHPR?
A voltage sensor that senses the arrival of a muscle AP as it tracks along the t-tubule signalling the RYR receptors to open releasing Ca++ from the SR
What is the shuttle protein for calcium in skeletal muscle?
Calsequestrin
What is sarcalumenin?
Facilitates moving calcium from areas where its taken up by SERCA to areas for release in the cisternae region
What does SERCA stand for?
Sarcoplasmic Endoplasmic Reticulum Calcium ATPase
What does the binding of troponin C to calcium result in?
Uncovers myosin binding sites so that myosin binds to actin and a cross-bridge can now form
How does the cross-bridge cycle work?
At rest, myosin and actin are detached and myosin is in energised state
AP triggers release of Ca++ from SR binding to troponin C allowing interaction
Inorganic phosphate detaches from myosin head allowing the sliding of the 2 filaments and pulls the actin filament towards the centre of sarcomere (power stroke)
ATP attaches to myosin, detaching it from actin
Muscle relaxes and Ca++ pumped into SR
ATP hydrolysed
Explain isotonic muscle contraction.
Constant force
Muscle shortens and can move the load
Muscle length can be measured
Explain isometric muscle contraction.
Constant length
Muscle unable to shorten
Force generated is measured
What is the optimal resting length for the sarcomere in order to achieve maximum strength of contraction?
2.25 microns
What is the relationship between velocity of muscle contraction and the load on the muscle?
Varies inversely with each other
How do we modulate the force of skeletal muscle contraction?
Spatial summation
tetany
What is tetany?
Sustained contraction of the muscle at high levels of stimulation
In spatial summation, what type of muscle fibres tend to be recruited first?
Slow twitch muscle fibers
What is muscle fatigue?
Reduced ability of muscle to generate power
