Electron Microscopic Observations on the Innervation of the Smooth Muscle

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Abstract
Intestinal smooth muscles (the rat and guinea pig ileum, guinea pig taenia coli and rabbit colon), and urogenital smooth muscles (vas deferens, seminal vesicle, urinary bladder and ureter of the rat and guinea pig) were observed with the electron microscope to study the innervation of the autonomic nerve in the smooth muscle tissue. In the intestinal smooth muscles, the nerve endings occurred as a large aggregate, but no single axon was present. In the urogenital smooth muscles, an abundant distribution of the single axons was observed among the smooth muscle fibers. The synaptic vesicles found in the axons of the intestinal smooth muscles were mainly agranular, whereas those of the urogenital smooth muscles were granular vesicles partly mixed with agranular ones. In the smooth muscle layer of the rabbit colon, the nerve endings contained characteristically large granular vesicles that could not be observed usually in other smooth muscle tissues.