The intramural nerve cells in the duodenum are very low in development as those in the stomach, ⁵⁾ by white rats, so that they cannot be classified into the two kinds of Dogiel's Type I and Type II cells. But the fact that they are multipolar seems to indicate that they are sympapathetic. As the sympathetic and parasympathetic nerve fibres as well as the peripheral parts of the long nerve processes of the nerve cells in the walls are in anastomosis with each other, they cannot be distinguished histologically. The end apparatus of these vegetative nerve fibres is represented by the Stöhr's terminalreticulum, which is sympathetic and parasympathetic at the same time and stands to supply all the tissue- cells by contact.
In the duodenal walls of white rat are found sensory nerve fibres and their terminations, which presumably originate in the comparatively abundant sensory cerebro-spinal nerve fibres of the splanchnic nerves.
The sensory endings are classified into the three types of branched endings, glomerular endings and snake-like endings. The branched endings constitute the majority and are represented as comparatively widely diffused endings found also in the tela submucosa, but principally in the lamina propria mucosae. These endings consist of rather large sized main fibres, after losing their myelin, dividing into some branches which show in places neurofibril expansions and peculiar windings, and end sharply or bluntly. In the submucosa, these endings frequently reach the duodenal glands or run into lymphatic nodes. In the propria mucosae, they run around the crypts or further into the villi and even close up to the epithelium.
The glomerular endings are very rarely formed in the submucosa. They consist of thicker nerve fibres showing change in size and winding courses. They have some special syncytial nuclei but lack a connective tissue mantle.
The snake-like endings consist of sensory nerve fibres of medium size, which, upon becoming unmyelinated, run in snake-like or wave-like windings for a comparatively long course and terminate sharply or bluntly. Sometimes, these endings show a partial glomerular course.
The existence of sensory nerve terminations in the duodenum, as described in the above, shows that, here, as well as in the stomach, ⁵⁾ transmission of sensory stimuli is effected by way of cerebro-spinal nerve fibres. The reason of their existence presumably consists, physiologically, in the formation of a reflex arc to promote secretion of digestive fluids, and pathologically, in the causing of peculiar duodenal pains.