Muscle fibers show a range of responses to different levels of stimulation because A) each muscle fiber contraction is "all or none." B) the availability of Ca²⁺ sets an upper limit to the strength of the contraction. C) a new contraction can occur only after the resting condition is reached. D) following stimulation, the fiber stays contracted. E) individual twitches in the same fiber can summate.

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Quizplus · Accepted Answer

Individual twitches in the same fiber can summate, meaning that if a second stimulus is applied before the fiber has fully relaxed from the first stimulus, the second twitch will add to the first, resulting in a stronger overall contraction. This allows for a range of responses to different levels of stimulation.

Muscle Fibers Show a Range of Responses to Different Levels