Answer:
Once initiated, an action potential is propagated the entire distance from the upper motor neuron to the muscle cell.
Explanation:
A motor neuron is a neuron which transmits the electrical signals from the CNS to the effector muscle. The motor neuron transmits the signals in the form of neurotransmitters at synapse like the Glutamate, acetylcholine.
The direction of the impulse transmission is unidirectional but the impulse is not transmitted or propagated the entire distance from the upper neuron to muscle but involves many neurons where the signals when reaches the terminal transfers the signals to the next neuron only when the neurotransmitter released is to the excitatory level.
Thus, the selected option is correct.