Which statement about skeletal muscle is true?
A) The fewer muscle fibers a motor neuron innervates, the larger the forces produced by a muscle.
B) A single action potential stimulates multiple twitches.
C) Twitches sum when action potentials arrive well separated in time.
D) The number of motor units activated and the frequency with which the motor units fire determine the level of tension in a muscle.
E) Summing of twitches occurs because ATP pumps in the sarcoplasmic reticulum are unable to clear ATP from the sarcoplasm between action potentials.

Question

Quizplus · Accepted Answer

The number of motor units activated (recruitment) and the frequency with which they fire (summing of twitches) determine the level of tension in a muscle. The size of a motor unit does not necessarily correspond to the amount of force it can produce, as larger motor units may contain only small, fatigue-resistant fibers. The summing of twitches occurs due to the addition of more cross-bridge interactions between actin and myosin in individual muscle fibers, leading to stronger contractions. ATP pumps in the sarcoplasmic reticulum are responsible for removing calcium ions, not ATP, from the sarcoplasm between action potentials.

Which Statement About Skeletal Muscle Is True