TEM of striated muscle and nerve fibers. Histology-nervous system. Colorized transmission electron micrograph of motor nerve and two plates on adjacent muscle fibers. The motor neuron, or nerve, terminates in branching fibers, which end in a cluster of swelling boutons called an end plate. The end plate is recessed into the surface of the muscle cell. When activated, the boutons release neurotransmitter chemicals that travel across the synapse between cells to interact with receptor in the muscle cells.