Twitch summation can be achieved through any of the mentioned mechanisms, including gradation of muscle contraction, increased release of Ca₂₊, increasing frequency of firing within a muscle, and more cross bridges binding to actin. Therefore, option E, which includes all of the above characteristics, is the best choice.

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Twitch Summation

Question 41

Multiple Choice

Twitch summation

A) is a means by which gradation of muscle contraction may be accomplished
B) results from the additional release of Ca₂₊ within the cytosol of muscle fibers
C) results from increasing the frequency at which motor units are firing within a muscle
D) results from more cross bridges binding to actin within muscle fibers
E) has all of the above characteristics

Correct Answer: