L11 Skeletal Muscle Flashcards
Modulation of force generation in skeletal muscle
Length/tension relationships
Summation
Motor unit recruitment
Fiber cross-sectional area ( atrophy/hypertrophy)
Fiber type (fast-twitch, slow-twitch)
Isometric contraction
Same length
Lift something and just hold it up
Generate force but no appreciable shortening of muscle length (no work )
Isotonic contraction
Same tension
Contractions that result in shortening of muscle length against a constant load (work done)
Passive tension
Tension developed by simply stretching a muscle (no stimulation)
Total tension
Tension developed when a muscle stimulated at different muscle lengths (preload)
Sum of active and passive tensions
Active tension
Determined by difference in tension
Active=total -passive
Tells what percentage due to cross bridge formation
Peak active tension
Optimal length (Lo)
In vivo is resting length
Max point we can have max amount of cross bridges
Maximal tension
Can be developed at optimal length b/c this is the point of optional thin and thick filament cross bridge binding sites
What’s resting SKELETAL muscle length near in the body?
Lo optimal length !
Single muscle twitch
A single action potential in a muscle fiber produces a brief, weak contraction
Frequency of stimulation influences the
Tension developed by each fiber
Whats Twitch summation and what does it result from ?
Muscle fiber and re-stimulated before it completely relaxed
A sustained elevation in cytosolic Ca
Tetanus
Muscle fiber stimulated so rapidly it does not have an opportunity to relax at all
Maximal sustained contraction
Motor unit
Motor neuron and innervated fibers
All fibers in a motor unit contract “all or none”
What do muscle fibers are into?
What do they produce?
Whole muscles
produce contractions of variable grades -“graded activation”
What does graded force development within a whole
Muscle depend on ?
Extent of motor unit recruitment
Little force- recruit small, slow motor units
Greater force- recruit large, fast motor units
Muscle fiber types in humans
Myosin type I
Myosin type IIa
Myosin type IIx
Fiber type proportion varies among muscles
One motor unit always has
The same fiber types!
Type I
Slow-twitch (more oxidative, more mitochondria)
Fatigue slowly
Red in color
Supplied with capillaries
Twitch tension low
Type IIx
Fast twitch (fast oxidative , more dependent on glycolysis)
Fatigue rapidly
Larger diameter
High glycogen content
White
Tension twitch high
Type IIa
Fast twitch (oxidative/glycolysis)
Low resistance to fatigue
Intermediate color
Tension twitch moderate
Order of resistance to fatigue of muscle fiber types
I>IIa>IIx
Which muscle fiber type is recruited first?
Type I and small motor units
Average persons fiber types
Mostly slow type I
Smaller amount type IIa
Even smaller amount type IIx
As endurance based athleticism increases how do muscle fiber types change?
Slow type I increases
Type IIa and IIx decrease
How do muscle fibers change in sprinters and sedentary people change?
Fast type IIx increases
Slow type I and fast type IIa decrease
An extreme endurance athlete has which muscle fibers?
Almost all slow type I
Very small amount type IIa
A person with small cord injury has what ratio of muscle fibers?
Almost none of slow type I
Equal ratio of fast types IIa and IIx
