The first motor neuron in the parasympathetic division is located in motor nuclei in the brain or in sacral spinal cord segments. It uses acetylcholine as its neurotransmitter.
The second motor neuron is in peripheral head ganglia or terminal ganglia in the thorax and abdomen. These are sensitive to acetylcholine as well as to other substances, such as monoamines, amino acids, and peptides. This motor neuron also uses acetylcholine as its neurotransmitter, but others are known to exist (in fact, coexist), many of which are peptides, monoamines, amino acids, and purines.
The terminal ganglia of the abdominal viscera are also known as the enteric ganglia (and make up what is often considered a third division of the ANS). The enteric ganglia are numerous and exist in an extensive network of fiber connections. There usually are two layers of networked ganglia - the submucosal layer and the myenteric layer.