Electron Microscopic Studies of Nerve Endings in the Mucous Membrane of the Human Intestine

The mucous membrane of the human small intestine and appendix were fixed in 1% osmium tetroxide buffered with veronal acetate (pH 7.25), embedded in styrene-methacrylate and, after sectioning, stained with sodium hydroplumbite for electron microscopy. The results obtained are as follows:1. Nerve bundles entering the mucosae of the human small intestine and appendix divide into many fine branches, each consisting of several axons with a Schwann cell sheath covered with basement membrane. Each axon is usually hung by one mesaxon,108Nerve Endings in Mucous Membrane of Human Intestine 419. but sometimes two or more axons are held in common one and the same mesaxon.2. As the fine nerve bundles pass into the muscularis mucosae,. some of the axons in the nerve bundle lose the covering of the Schwann cell and are markedly swollen to form the vesiculated nerve processes which lie along the outer surface of the fine nerve bundle and are filled with a large number of agranular synaptic vesicles without granules, several granular vesicles containing dense granules and mitochondria. A large part of the surface of the vesiculated nerve process is naked and shows juxtaposition to the smooth muscle cells at a relatively large distance of 2,000 to 3,000 Å, The vesiculated nerve process of this kind would represent the possibility of presence of the diffuse innervation in the muscularis. mucosae by ' Synapse auf Distanz ' suggested by Jabonero.3. In the propria of mucosae the fine nerve bundles lie between the vessels, intestinal glands and proper cells. The fine axons in. the nerve bundle lose their sheath and pass into grooves on the surf ace of the interstitial cells of Cajal to form slightly swollen expansions which contain many agranular synaptic vesicles. Vesiculated nerve processes of this kind involve a close apposition of the surface membrane of the nerve process and that of the interstitial cell. They are separated by an interval ranging from 120 to-200 Å in width and show an increased density in the contiguous. field of the synaptic junction. The agranular vesicles appear as a cluster polarized toward the closely apposed synaptic membranes.. Basement membrane material does not extend into the cleft of this. type of synaptic junction.4. The nature of both types of vesiculated nerve processes. found here with reference to the transmitter substances, acetylcholine and catechol amines, which are thought to be related to tha agranular and granular synaptic vesicles respectively, are briefly discussed.