EM of synaptic vesicles at a neuromuscular junction. The terminal end of a nerve cell contains many small, smooth-surfaced synaptic vesicles (arrows). They hold the neurotransmitter acetylcholine, which is discharged by exocytosis into the synaptic cleft. Mitochondria (Mi), which supply energy, are in the cytoplasm of both the nerve cell and muscle cell. 60,000×.