Which of the following will respond to a threshold stimulus with an all-or-none contraction?

A) A single muscle fiber
B) A single motor unit
C) A whole muscle
D) Both a single muscle fiber and a single motor unit are correct.
E) A single muscle fiber, a single motor unit, and a whole muscle are all correct.

Threshold Stimulus

Stimulus resulting in a local potential just large enough to reach threshold and produce an action potential.

All-Or-None Contraction

A principle stating that a nerve or muscle fiber responds completely or not at all to a stimulus once the stimulus reaches a threshold value.

Muscle Fiber

A single, elongated muscle cell that can contract in response to stimulation.