Question

abrupt change from a negative to a positive charge of a nerve cell
motor neuron
axon terminal
action potential
muscle fiber
muscle contraction

Explanation:

An action potential is the abrupt change from a negative to a positive charge (depolarization) and then back to negative (repolarization) in a nerve cell. A motor neuron is a type of nerve - cell that transmits signals to muscles. An axon terminal is the end - part of an axon that releases neurotransmitters. Muscle fibers are cells that make up muscles and muscle contraction is the process of muscles shortening.

Answer:

C. action potential