During development embryonic cells will fuse to form muscle fibers. this will result in .

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.