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What are the limitations to using mATPase histochemistry for fiber typing skeletal muscle?
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You can only see 3 different colors as opposed to if there is hybrid fiber types
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List 2 reasons why fast-twitch fibers contract faster than slow-twitch fibers
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1)High SR development
2) Faster ATPase
3) 50ms contraction for Type II than 110ms for Type 1
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What is the most abundant (i.e., highest concentration) protein in skeletal muscle?
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Myosin
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What is the role of ATP in muscle contraction? Be specific
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1) ATP binds myosin, separates cross bridges
2) ATP broken down by ATPase
3) Repositions head
4)Myosin binds to new actin
5)Release of ADP and Pi cause power stroke
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Which fiber type produces the most power? Why?
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Type IIx because it's speed is 50ms which is quicker than Type I which is 110ms
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What is the primary role of Ca++ during a muscle contraction?
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Ca++ is released from the SR due to an electrical impulse, binds to troponin causing a shift to tropomyosin, myosin head then attaches to actin.
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What is the actin:myosin ratio in normal human skeletal muscle ?
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6:1
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What percentage of skeletal muscle is protein?
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20%
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If the intramuscular concentration of a substrate is 100mM per unit muscle wet weight, what would the concentration of that substrate be when expressed per unit muscle dry weight?
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100mM x 400 = 400mM per unit muscle dry weight
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What percentage of the contractile protein is myosin?
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~50%
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What percentage of the contractile protein is actin?
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~25%
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Compare/contrast the two most commonly used approaches for determining muscle fiber types in human skeletal muscle.
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Gel Electrophoresis: This type of muscle fiber typing uses electrodes to determine different types of fibers based on MHC. More clear than histomychemistry because it is able to see hybrid fiber types. Tells you the make up of the muscle not the size of the muscle.
Histomychemistry: can only be used to see 3 fiber types, it is not able to see hybrids. Based on mATPase.
Both: can determine muscle fiber types
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Define hybrid muscle fibers and their in human skeletal muscle. How do these fibers respond to changes in physical activity patterns?
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Hybrid muscle fibers are a combination of muscle fibers such as; type I/type IIa or type IIa/type IIx. These hybrid muscles allow for a greater change in fiber type. When there is an increase in a persons physical activity there is a decrease in the amount of hybrid fibers. Hybrid fibers on the other hand will increase due to inactivity.
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What is the most sampled muscle in human exercise studies? Why is this muscle commonly assessed?
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The most sampled muscle in human exercise studied is the Vastus Lateralis. This muscle is commonly assessed because it's easily accessable and is also a common muscle used in many sports, so a sport such as cross country can be compared and contrasted with a sport such as basketball. It is also easy to get to.
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Define motor unit and describe the pattern of motor unit recruitment.
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Motor unit is a motor neuron and all the muscle fibers it intervates. The pattern of motor unit recruiment is based on the size principle. the size principle, state that the order of recruiment of motor units is directly related to motor neuron size. Motor units with smaller motor neurons will be recruited first.
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