Transmission electron micrograph (TEM) of the ultrastructure of unmyelinated nerve fibres in the myenteric (Auerbach's) plexus of the gastrointestinal tract. The peripheral tissue is smooth muscle which is supplied by these nerves. Mitochondria are seen in the axons and in several peripheral axons, aggregations of tiny vesicles are noted in axon terminals. Vesicles contain neurotransmitters such as acetylcholine that regulates muscle contraction of the gut. Magnification: x5,000 when width printed at 10cm.