Muscle relaxation requires __________.
ATP
Muscle relaxation requires ATP for two reasons. First, myosin releases actin in order to bind ATP. Second, ATP is required in order to pump calcium against its concentration gradient into the sarcoplasmic reticulum via the calcium ATPase.
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The role of calcium is to bind to the troponin complex, which moves tropomyosin aside, making the myosin binding sites available on the actin filament.
The removal of calcium contributes to muscle relaxation because the tropomyosin covers the myosin binding sites on the actin filament.
When the myosin head hydrolyzes ATP to ADP and Pi, the released energy is utilized by the myosin molecule to
re-cock the head.
___________ is a protein that calcium binds to, causing tropomyosin to move aside, making the myosin binding sites available on the actin filament.
Troponin
When an action potential travels along the sarcolemma of a muscle cell __________.
DHP receptors in the T-tubule undergo a conformational change and Ca2+ flows down its concentration gradient through the ryanodine receptors
Once the calcium enters the cytosol, it binds to the troponin complex, causing tropomyosin to move aside in order to expose the myosin binding sites on the actin filament. Now, it is possible for crossbridge cycling to occur.
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During a prolonged bout of continuous exercise (longer than 30 minutes), ATP stores are replenished by __________.
fatty acids in the bloodstream
During complete tetanus __________.
cytosolic calcium levels are high enough to saturate all the troponin molecules, action potential frequency is higher than the fused muscle twitch frequency, and action potential frequency is higher than the fused muscle twitch frequency
As the load on a muscle increases, which of the following also increase(s)?
Latent period
Put the events of the crossbridge cycle in the correct order, starting with the binding of myosin to actin:
a. binding of ATP
b. release of Pi
c. release of ADP
d. power stroke
b, d, c, a
The troponin complex in thin filaments can bind __________.
tropomyosin, calcium, and actin
Which of the following statements about muscle contractions is(are) true?
The sarcomeres shorten during isometric and isotonic contractions.
High capillary density, high myoglobin content, and high resistance to fatigue describe which of the following skeletal muscle types?
Red, slow oxidative muscle fibers
The latent period is due to the time it takes for __________.
excitation-contraction coupling
The _________ is the time between the action potential in the muscle cell and muscle contraction
latent period
Which of the following statements about muscle contraction is(are) true?
Each myosin head completes about five crossbridge cycles per second, but each thick filament has hundreds of myosin heads.
Molecules that are more likely to be found in higher concentrations in a fast glycolytic fiber include __________.
pyruvate and lactic acid
Which of the following is(are) true about small motor units?
They tend to be recruited first during a contraction and they generate less tension than large motor units.
Skeletal muscles with the most endurance (resistance to fatigue) are __________ in color.
red
The force generated by a muscle depends directly or indirectly on the __________.
force generated by individual muscle fibers, number of muscle fibers contracting, and number of active crossbridges formed
When myosin is bound to actin during the crossbridge cycle __________.
calcium is bound to the troponin complex and myosin is in its high-energy form
Thick filaments have __________.
ATPase activity and actin binding sites
Muscle tension decreases at short muscle lengths because __________.
the thin filaments at opposite ends of the sarcomere overlap and the Z lines come into contact with the thick filaments
The functional unit within a muscle fiber is called a sarcomere. Which of the following does not make up part of the sarcomere?
Myofibril