Force generation, energy usage and fibre types Flashcards
What is excitation contraction coupling?
Linkage between excitation of the muscle fibre membrane and the onset of contraction
What does the ability of a muscle fibre to generate force and movement depend on?
The interaction of the contractile proteins actin and myosin
In the sliding filament mechanism, which band(s) and/or zone(s) are reduced?
- The I band
* The H zone
In the sliding filament mechanism, what zone(s) and/or band(s) remain unchanged
• The A band
What are the structural proteins in skeletal muscle?
- Titin (connection)
- Z-line protein (alpha-actinin)
- M-line proteins (myomesin, M-protein)
- Nebulin
What are the contractile proteins in muscle?
- Actin
- Myosin
- Tropomyosin
- Troponin complex
What is the role of Nebulin?
It helps to align actin
What is the role of Titin?
It provides elasticity and stabilises myosin
Describe the cross-bridge cycle
- Ca++ increases Cross-bridge binds to actin, creating tension within the muscle
- The cross bridge moves
- ATP binds to the myosin causing cross-bridge to detach
- Hydrolysis of ATP energises the cross-bridge
What enzymes are involved in the breakdown of ATP to ADP + Pi in the contraction
- Ca2+ ATP-ase
* Myosin ATP-ase
How much ATP do the muscles contain?
4mM/kg
What is rigor mortis?
Stiffening of skeletal muscles after death
When does rigor mortis begin and when is it at its maximum?
- 3-4 hours after death
* Max after 12 hours
Why does rigor mortis happen?
- Cells accumulate calcium
* In the absence of ATP cross bridges can bind to the actin but the cross-bridge linkage is irreversible
What does contraction of a muscle refer to?
The activation of the force-generating sites within muscle fibres- the cross bridges
What are the 3 ways a muscle fibre can form ATP?
- Phosphorylation of ADP by creatine phosphate
- Oxidative phosphorylation of ADP in the mitochondria
- Phosphorylation of ADP by the glyhcotic pathway in the cytosol
What are muscle fibres classified on the basis of?
- Maximal velocities of shortening
* Major pathway they use to form ATP- oxidative or glycolytic
Describe oxidative muscle fibres
- More mitochondria so have a higher capacity for oxidative phosphorylation
- Dependent on blood flow to deliver oxygen and fuel molecules
- Contain myoglobin
- Appear darker
- Muscles containing more of the oxidative muscle fibres are used for long term contraction e.g. muscles used for standing
Describe glycolytic muscle fibres
- Few mitochondria
- High concentration of glycolytic enzymes and large store of glycogen
- Used for quick bursts of activity
- Muscles containing a lot of these fibres are known as ‘white’
Type I
Slow oxidative fibres
• Red
• Combine low myosin ATP-ase activity with high oxidative capacity
Type IIa
Fast oxidative fibres
• Pink
• Combines high myosin ATP-ase activity with high oxidative capacity and intermediate glycolytic capacity
Type IIb
Fast glycolytic fibres
• White
• Combines high myosin ATP are activity with high glycolytic capacity
Describe what happens in full muscle contraction in terms of the contraction of the muscle fibres
- Slow oxidative fibres contract first
- Fast oxidative fibres contract second
- Fast glycolytic fibres contract last
What factors determine muscle tension?
1) Tension developed by each type of muscle fibre
• Action potenital frequency
• Fibre length
• Fibre diameter
• Fatigue
2) Number of active fibres
• Number of fibres per motor units
• Number of active motor units
What does the control of shortening velocity depend on?
- Load of muscle
- Type of motor unit
- Number of motor units
How does muscle adapt to exercise
Increase in the amount of contractile activity increases the size of the muscle fibres and increases their capacity for ATP production
What are the two types of atrophy?
- Disuse atrophy e.g. an arm in a cast
* Denervation atrophy (nerve damage resulting in loss of function)
