Skeletal 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 fibers stay contracted. E) individual twitches in quick succession in the same fiber can undergo summation.

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Quizplus · Accepted Answer

Skeletal muscle fibers can undergo summation by having individual twitches in quick succession. This means that if a fiber is stimulated again before it has fully relaxed from the first twitch, the second twitch can add on to the tension generated by the first twitch. Therefore, the response of a muscle fiber to different levels of stimulation can vary depending on how many twitches occur and how close together they are.

Skeletal Muscle Fibers Show a Range of Responses to Different