| Abstract: | An electron microscopical investigation was made of neuronal terminals in operatively removed human duodenum and jejunum. No intraepithelial neuronal elements were found. The lamina propria mucosae, submucosa and muscular layer possessed, in addition to large bundles of unmyelinated nerve fibers, small ones consisting of three or four axons wrapped by infoldings of one Schwann cell. Some of these axons were light; others contained mitochondria and clear vesicles measuring 200–500 Å across. Still other axons had dense-cored vesicles with a diameter ～ 700 Å. The plasma membranes of vesiculated axons were not thickened and only in part invested by the Schwann cell, but were covered by a basement membrane. Such profiles were interpreted as nerve terminals, and were separated from fibers of the muscularis mucosae, bases of epithelial cells and submucous capillaries by interspaces measuring 5,000–6,800 Å. The gap between neuronal terminals and smooth muscle in the muscular wall was smaller (900 Å, more often 1,500–3,000 Å). The myenteric plexus contained nerve bundles consisting of the usual axons and of preterminals; some of the latter contained small clear vesicles, others predominantly larger granulated vesicles, and still others a mixture of both types of vesicles. The similarities and differences of neuronal terminals occurring in animals and in man were pointed out. The significance of the findings of this study was discussed in the light of current concepts of the physiology of autonomic nerve transmission. |
