Download Skeletal muscle fiber types and length-tension

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SUMMATION OF CONTRACTIONS
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The contractile mechanism does not have a refractory period; re-stimulation of an ongoing contraction will
produce another contraction on top of the existing one.
With rapidly repeated stimulation, activation of the contractile response occurs repeated before any
relaxation has occurred
This constant contraction is called a TETANIC CONTRACTION
COMPLETE TETANUS = no relaxation at all
INCOMPLETE TETANUS = periods of incomplete relaxation take place between periods of contraction
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During complete tetanus, the tension developed is about 4 times the tension of individual twitch contractions
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determined by the twitch duration of that particular muscle
if the twitch duration is 10 milliseconds, you need to stimulate the muscle MORE FREQUENTLY then every
10ms in order for summation to occur
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HOW OFTEN MUST I STIMULATE THE MUSCLE TO GET TETANUS?
MUSCLE LENGTH, TENSION, AND VELOCITY OF CONTRACTION
TOTAL TENSION = tension developed when the muscle contracts
isometrically (without changing its length)
PASSIVE TENSION = tension in unstimulated muscle
ACTIVE TENSION = actual amount of tension generated by the contractile
process
o = the difference between passive tension and total tension at a
given length
o The length of muscle at which the active tension is maximal we
call the RESTING LENGTH
o This is because In the body, most muscles achieve maximal
active tension at a normal resting length
Total tension
Active tension
Tension
This makes sense because:
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Passive tension
Length
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When muscle is stretched, the overlap between actin and myosin
filaments is reduced, and so there is less cross-linkages (so the
force generated is less)
When the muscle is squished to some length shorter than resting
length, there is too much overlap between actin and myosin
filaments, and thus there is less room for actin to move (less
contraction is possible)
THE VELOCITY OF MUSCLE CONTRACTION VARIES INVERSELY WITH THE LOAD ON THE MUSCLE
AT A GIVEN LOAD, THE VELOCITY IS MAXIMAL AT RESTING LENGTH, AND DECLINES IF THE MUSCLE IS SHORTER
OR LONGER
MUSCLE FIBER TYPES
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THERE ARE 3 MAIN TYPES:
Type 1
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slow oxidative fibers
moderate SERCA activity, small diameter, slow glycolytic capacity
high OXIDATIVE capacity, more mitochondria, higher capillary density and myoglobin content
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fast oxidative and glycolytic fibers
high capacity SERCA pumps, large diameter fibers, high glycolytic capacity
high oxidative capacity
Type 2a
Type 2b
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fast glycolytic fibers
also large, also high-capacity calcium pump, also high glycolytic capacity, but much less oxidative
capacity
there are numerous different forms of myosin tropomyosin and troponin, but only one form of actin
Type 2a and 2b fibers are most susceptible to exercise- they grow fastest
Type 1 fibers are most susceptible to inactivity- they atrophy fastest