Force generation, energy usage and fibre types Flashcards
How is membrane potential maintained?
Na+/K+ ATPase in sarcolemma maintains Na+ and K+ gradients, allowing production and propagation of action potentials
How is Ca2+ gradient maintained?
Active transport of calcium ions into the sarcoplasmic reticulum - lowering
What is the power stroke
Hydrolysis of ATP by myosin-ATPase energises the cross-bridge
What is cross bridge dissociation?
Binding of ATP to myosin dissociates cross-bridges bound to actin
Describe energy metabolism
- Creatine phosphate - rapid ATP formation at the onset of muscle contraction
- Glycolysis - anaerobic ( fast rate of ATP generation from glucose/glycogen)
- Oxidative phosphorylation - aerobic (supplies most amount of ATP per glucose molecule and power contraction for hours)
Describe events during cross bridge formation to generate sarcomere shortening
- ATP binding
- ATP hydrolysis
- Cross bridge formation
- Release of Pi from myosin
- Power stroke
- ADP release
What are the types of skeletal muscle fibres
- Type IIB/IIX
- Type IIA
- Type I
Describe Type IIB/IIX muscle fibres
- High glycolytic
- Anaerobic
- Low in myoglobin
- Fast
Describe type IIA muscle fibre
Mixture of fast oxidative capacity, glycolytic capacity and fast ATPase activity
Describe Type I muscle fibres
- Oxidative
- Aerobic
- High in myoglobin
How are skeletal muscle fibres classified?
- Maximal velocities of contraction
- Major pathway for generation of ATP
What are differences in skeletal muscle fibres
- Different muscle types have different isotypes of myosin ATPases
- Different maximal rates of cross bridge cycling
What are the differences in physiological features in slow oxidative fibres
- Number of mitochondria
- Amount of myoglobin
- Blood vessels
What are the differences in fast glycolytic fibres?
- Stores of glycogen/ glycolytic enzymes / creatine phosphate
- Size
How do skeletal muscles receive stimuli from a motor neurone
receive stimuli from a motor neurone - each myofiber/ muscle cell has its own neuromuscular junction
How does the duration of contraction differ?
- Duration of contraction differs depending on fibre type composition of individual muscles
- Highly adapted to function
- Ocular - extremely rapid
- Gastrocnemius - moderately rapid
- Soleus - relatively slow
What are motor units?
- A single motor neurone innervates multiple muscle fibres
- All fibres innervated by a single neurone are called a motor unit
- Generally - small muscles with fine control have fewer muscle fibres per neurone
- Conversley large muscles may have hundreds of fibres in a motor unit
What is the size principle?
- Force contraction depends on
- Number of motor units recruited
- Frequency of action potentials
How are motor units recruited?
- Motor units recruited in a progressive way from small to large
-
Small motor units are:
- More excitable
- Conduct action potentials more slowly
- Typically type I slow fibres
-
Large motor units are:
- Less excitable
- Conduct action potentials more rapidly
- Typically type II fast fibres
What is muscle tension
Force exerted by a contracting muscle is known as muscle tension
What is the load
Force exerted by an object to be moved is called the load
What must a muscle do to shorten?
Overcome the load force
Describe the Length tension relationship
- Length-tension is directly related to the overlap between the actin and myosin within the sarcomere
- Tension generated at different degrees of overlap and sarcomere length
What happens at D
Zero tension-No actin myosin overlap
What happens at point C
Maximum tension - actin overlaps all pf the cross bridges on myosin full tension maintained until point B
What happens at point B
Maximum tension - the ends of the two actin filaments begin to overlap each other in addition to overlapping the myosin
What happens at point A
As the sarcomere shortens further, the two Z discs about the myosin - tension drops close to zero
Explain the tension-velocity relationship
- Full muscle contraction is rapid with no tension
- When tension is applied contraction velocity decreases with increasing tension
- When the tension equals the maximum velocity is zero ( isometric contraction)
