| Abstract: | The fine structure of the neuromuscular contacts of arterioles and small arteries from the jejunum and mesentery of the rat has been studied. There is a rich innervation of these vessels, consisting of bundles of axons in the adventitia around the vessels. In the typical sympathetic neuromuscular contact on a small blood vessel, the axon bundle is loose, the Schwann cell cover is deficient, the neuromuscular distance is less than 1,500 Å, the basement membranes of axon and smooth muscle cell are fused together, and the axon tends to follow the contour of the smooth muscle cell. However, it is not possible to be certain that these criteria are essential for a true functional neuromuscular contact. In particular, it appears from the structural findings that a neuromuscular distance of 2,000–3,000 Å or more could well be compatible with effective neuromuscular transmission. Smooth muscle cells in arterioles often have multiple innervation, and an axon probably innervates more than one smooth muscle cell. Occasional axons contain mainly or solely vesicles of the “large granular” type. |
