A neuromuscular junction (NMJ) is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract. In vertebrates, the signal passes through the neuromuscular junction via the neurotransmitter acetylcholine.

The neuromuscular junction is the location where the neuron activates muscle to contract. This is a step in the excitation-contraction coupling of skeletal muscle.

Acetylcholine is a neurotransmitter synthesized in the human body from dietary choline and acetyl-CoA (ACoA). One of the first neurotransmitters discovered, the substance was originally referred to as "vagusstoff" because it was found to be released by the stimulation of the vagus nerve. Later, it was established that acetylcholine is, in fact, important in the stimulation of all muscle tissue and that its action may be either excitatory or inhibitory, depending on a number of factors. Within the body, the synaptic action of acetylcholine usually quickly comes to a halt, the neurotransmitter naturally breaking down soon after its release. However, some nerve gases are designed to thwart this breakdown, causing prolonged stimulation of the receptor cells and resulting in severe muscle spasms.