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In skeletal muscle, minimum unit of contraction is a __, which is measured in terms of __, or force it generates
twitch; tension
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A single action potential generates __. Force generated depends on __
- a single twitch;
- how many fibers are in the motor unit
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Tension generated by entire muscle depends on:
- number of motor units activated
- frequency at which motor units are firing
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If action potentials are close together in time, the twitches are __, tension __
summed; increases
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Twitches sum because __
Ca2+ pumps can not clear Ca2+ from sarcoplasm before next action potential arrives
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__ occurs when action potentials are so frequent there is always Ca2+ in the sarcoplasm
Tetanus
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How long muscle fiber can sustain tetanus contraction depends on __
ATP supply
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__ is needed to break the actin-myosin bonds, and "re-cock" the myosin heads
ATP
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To maintain contraction, actin-myosin bonds have to __
keep cycling
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Slow-twitch fibers are __ & contain __
- oxidative or red muscle;
- myoglobin (oxygen binding protein), many mitochondria, and is well-supplied with blood vessels
Maximum tension develops slowly.
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fiber that is highly resistant to fatigue. Muscles with high proportion of this type of fiber are good for aerobic work (e.g. long distance running, cycling, swimming, etc.)
slow-twitch fibers (oxidative or red muscle)
(page 41 & 42 on slide)
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__ fibers have reserves of glycogen & fat. They can produce ATP as long as oxygen is available.
Slow-twitch
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Fast-twitch fibers are __ & contain __
- glycolytic or white muscle;
- little or no myoglobin, fewer mitochondria, fewer blood vessels
Develop greater maximum tension faster
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fiber that develops fatigue more quickly & can't replenish ATP for prolonged contraction
fast-twitch fibers (glycolytic or white muscle)
(page 41 on slide)
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__ determines how much force can be generated (in muscles)
The resting length of the sarcomeres
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If the resting length of the sarcomeres is stretched, there is __, which means __
- less overlap between actin & myosin fibers;
- fewer cross-bridges & less force
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If the resting length of the sarcomeres is fully contracted, there is __
more space for shortening
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Muscles have 3 systems for supplying ATP for contractions:
- immediate system
- glycolytic system
- oxidative system
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The __ system uses preformed ATP & creatine phosphate
immediate
immediate system = ATP + CP
This system is exhausted within seconds.
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The __ metabolizes carbs to lactic acid & pyruvate.
glycolytic
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The __ system metabolizes carbs or fats to H2O & CO2.
oxidative
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Muscles contain __, which stores energy in a phosphate bond that can be transferred to ADP
creatine phosphate (CP)
- used in immediate system
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The __ enzymes are in the sarcoplasm. ATP generated is then rapidly available to myosin.
glycolytic
Glycolysis alone isn't very efficient. Lactic acid accumulates.
Immediate & glycolytic systems provide energy for less than one minute.
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__ systems produces large amounts of ATP, but takes place in the mitochondria. ATP must diffuse from the mitochondria to the myosin - rate is slower than other 2 systems
Oxidative
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