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Whole muscles can respond in a graded fashion to stimuli by varying Select one: a. the force of contraction of individual muscle fibers. b. the number of motor units recruited. c. the amplitude of the action potential. d. the frequency of stimulus. e. thresholds.
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b. number of motor units recruited
Motor unit recruitment is defined as the activation of several additional motor units resulting in a high contracting force in a muscle. A motor unit is composed of the excitatory muscle fibers and motor neurons only.
Motor neuron activation stimulates and contracts all the muscle fibers that the motor neurons receive. When only motor neurons are activated, it results in a weak but distributed contraction of the muscle. Activating more motor neurons will result in more muscle fibers, thus stronger muscle contraction.