Final answer:
The neuromuscular junction is composed of a motor neuron and a muscle fiber that work together to initiate muscle contraction.
Step-by-step explanation:
The neuromuscular junction is composed of a <1> motor neuron (presynaptic neuron) plus one <2> muscle fiber (postsynaptic cell). This specialized chemical synapse is where a motor neuron transmits a signal to a muscle fiber to initiate muscle contraction. Neuromuscular junctions consist of crucial elements, including the presynaptic element (axon terminals of the motor neuron), the neurotransmitter (acetylcholine), the synaptic cleft (the space where the neurotransmitter diffuses), receptor proteins (nicotinic acetylcholine receptors), the postsynaptic element (the sarcolemma of the muscle cell), and the mechanism for neurotransmitter elimination (via acetylcholinesterase).