Figure 5 - Parallel inhibitory and excitatory innervation of the esophageal smooth muscle.

The excitatory pathway includes vagal preganglionic neurons that are located in the rostral part of the DMN in the brainstem. These fibers project onto the excitatory postganglionic neurons that contain acetylcholine (ACh) and substance P. The inhibitory pathway includes preganglionic vagal fibers that are located in the caudal part of the DMN. These fibers project onto postganglionic inhibitory neurons that contain nitric oxide (NO), vasoactive intestinal peptide (VIP), adenosine triphosphate (ATP), and substance P (SP).