The stimulation of a motor neuron ultimately results in the release of an excitatory neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions

Glutamate.

Explanation:

"Glutamate" is the primary excitatory transmitter in the central nervous system. At a point where the axon of a motor neuron enters a muscle fibre, their is a structure called the "motor end-plate". When impulses reach an end plate, they set off chemical reactions which causes muscular contractions.

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