MSK 22 - Muscle Physiology-III Flashcards
Draw out the force vs length graph for a muscle, at a given starting length, lifting a weight. Draw the lines for both passive and total force and indicate what every point/region indicates.
For a muscle set at a specific starting length, will it be able to shorten more, less, or the same with heavier weights compared to lighter weights? Why?
Shorter.
Increasing the weight means the muscle has to generate more active force to begin moving the weight. The muscle does this by recruiting more crossbridges. This means that fewer crossbridges are available to shorten muscle. Therefore, the muscle cannot shorten as much as it can when moving lighter weights
For a muscle set to lift a given weight, will it be able to shorten more, less, or the same if the muscle starts out a longer length instead of a shorter length? Explain why.
Longer
At a longer length the muscle will have more preload, this means that less active force will need to be generated to begin moving the weight. This means more crossbridges will be available to shorten the muscle than if the muscle started at a shorter length.
Draw the force vs time graph for an isotonic contraction for two different weights. What is important to note about this graph.
On a length vs time graph of a muscle contraction, what indicates the contraction velocity?
What does the velocity vs afterload plot look life for a given muscle?
What determines the maximum contraction velocity of muscle?
How fast the crossbridge cycle can spin which is determined by myosin ATPase activity
Draw the velocity vs force graphs for the two types of skeletal muscle fibers. Indicate where Vmax and Fmax (max force) are. Why is there a difference?
Draw the velocity vs force graph for a muscle set at three different preloads.
What are the energy sources for skeletal muscle and how quickly are they available for use?
Since muscle contraction is “all or nothing,” how does skeletal muscle regulate force?
Temporal Summation - a single AP will not cause all the Ca++ to be released from the SR and that Ca++ will quickly be resequestered by SERCA. Therefore, several APs in succession can add up to cause much more Ca++ to be released from the SR and for cytosolic [Ca++] to stay higher longer
Spatial Summation - the recruitment of additional motor units within a muscle to develop more force
Why is temporal summation possible?
After the AP refractory period, there is period of time when the muscle has not relaxed completely. If another AP fires at this time then the second contraction will be stronger than the first.
What are the two primary causes of muscle fatigue? Explain both
