Skeletal Muscle Force Flashcards
Where is ATP used in contraction?
Ca2+ ATP-ase
Myosin ATP-ase
What pump allows production and propagation of action potential?
Sodium/potassium-ATPase in sarcolemma
Why is hydrolysis of ATP required by sodium/potassium-ATPase pump?
MAintains sodium and potassium gradients
What pump is responsible for for lowering calcium ions in cytoplasm?
Ca2+-ATPase in sarcoplasmic reticulum
Why Why does ATP need to be hydrolysed by calcium-ATPase?
Provide energy for active transport of calcium ions back into reticulum - to lower calcium concentration + allow relaxation
What enzyme provides energy of force generation?
Myosin-ATPase on myosin filament
Why does ATP need to be hydrolysed for myosin-ATPase?
To provide energy needed for cross-bridge formation
Significance of binding ATP to Myosin:
Dissociates cross-bridges
Allows bridges to repeat cycle activity
Cross-bridge cycle: stage 1 - ATP binding
Myosin in cocked state
Binding of ATP causes dissociation of actin-myosin complex
Cross-bridge cycle: stage 2 - ATP hydrolysis
ATP hydrolysed into ADP and phosphate ion
Myosin head in relaxed state
Cross-bridge cycle: stage 3 - Cross-bridge formation
Myosin head binds to new binding site on actin
Weak cross-bridge formed
Cross-bridge cycle: stage 4 - phosphate ion released
Phosphate ion is released from myosin head
Increase in strength of cross-bridge
Cross-bridge cycle: stage 5 - Power stroke
Conformational change in myosin head causes power stroke
ADP released
What regulates cross-bridge cycle?
Increase in calcium ions not ATP
3 ways of ATP formation in sketch muscle:
- Creatine phosphate
- Glycolysis
- Oxidative phosphorylation
What is creatine phosphate?
Stores phosphate ions that replace phosphate used in contraction
Rapid ATP formation
How much ATP does oxidative phosphorylation supply?
Most ATP in moderate activity levels
Location of oxidative phosphorylation:
Mitochondria
How much ATP does glycolysis supply?
Small quantities
Produces at higher rate - in higher intensity exercise
Location of glycolysis:
Cytosol
What can muscle force be determined by?
Number of individual muscle fibres stimulated
What does one motor neuron do?
Sends signal down to multiple muscle fibres
Spatial summation
What does amount of force generated from a muscle depend on?
Number of active fibres
Cross-sectional area
Initial resting length of muscle
Rate of shortening
Frequency of stimulation
Small vs large motor units: excitability
Small = more excitable
Large = less excitable
Small vs Large motor units: Action Potential conduction
Small = slower conduction
Large = faster conduction
Small vs Large motor units: how many fibres do they excite?
Small - fewer fibres that tend to be Type I
Large = many fibres that tend to be Type II
How are motor units recruited?
Smallest (weakest) to largest (strongest)
What are muscle fibres classified on the basis of?
Maximal velocities of shortening - fast or slow
Pathway they use to form ATP - oxidative or glycolytic
Why does form of myosin change maximal rate of using ATP?
Determines maximal rate of cross-bridge cycling and maximum shortening velocity
Fibres with many mitochondria:
High oxidative capacity - oxidative fibres
Fibres with few mitochondria:
High glycolytic capacity as high conc. of glycolytic enzymes
Large store of glycogen
Glycolytic fibres
Different types of skeletal muscle fibres:
Slow-oxidative fibres (Type 1)
Fast-oxidative-glycolytic fibres (Type IIa)
Fast-glycolytic fibres (Type IIb or IIx in human)
Slow-oxidative fibres:
Low myosin-ATPase activity
High oxidative capacity
Fast-oxidative-glycolytic fibres:
High myosin-ATPase activity
High oxidative capacity
Intermediate glycolytic capacity
Fast-glycolytic fibres:
High myosin-ATPase activity
High glycolytic capacity
2 ways Type I and II fibres can be identified:
Nature of myosin-ATPase
Amount of specific mitochondrial enzyme succinctly dehydrogenase
Nature of myosin-ATPase micrograph:
Type I = dark
Type II = light
Enzyme succinctly dehydrogenase micrograph:
Type I = dark
Type IIa = middle
Type IIx = light
What does one action potential result in?
Single skeletal muscle twitch
What does multiple action potentials result in?
Temporal summation - multiple muscle twitches before fully relaxing
What happens when multiple AP occur close together?
Frequency summation - infused tetanus
Plateau of contraction and relaxation
What happens when frequency of AP is super high?
Fuses Tetanus
Can’t identify individual contractions and relaxations
Type I - muscle twitches
Long twitch
Low tension
Not fatiguable
Type IIa - muscle twitch
Long twitch
More tension than type I
Has some fatigue resistance but will eventually fatigue
Type IIx - muscle twitch
Fast twitch
Lots of tension
Very fatiguable
WHat does contraction refer to?
Activation of force-generating sites within cross-bridges
Isometric contraction:
Muscle length fixed
Increase in tension but no shortening
Isotonic contraction:
Muscle length not fixed
Muscle shortening if tension greater than opposing load
What is length-tension relationship a result of?
Thick and thin filaments within sarcomeres
Total tension:
Tension measured at various muscle lengths during contraction
Passive tension:
Tension measured at any fixed length before contraction
Active tension:
Tension measured at any fixed length during contraction
What happens when applied load increases?
Decrease in shortening velocity
Why does velocity of shortening increase with limiting lighter load?
Same muscle length but fewer cross-bridges needed to oppose load
What does velocity of shortening limited by?
Time for ATP-consuming cross-bridge cycle to occur
