| Abstract: | The pharyngeal retractor muscle of the snailHelix lucorum is innervated by a pair of nerves containing axons of two types, for which there are two corresponding types of myoneural junctions with the muscle cells. The junctions of type I correspond to the thick axons. The terminals of these axons, which contain numerous spherical transparent vesicles (41±5 nm) and fewer vesicles of the dense-core type (67±3 nm), make contact mainly with noncontracting sarcoplasmic projections of the muscle cells. Junctions of type II correspond to thin axons, containing many granules. The terminals of these axons make contact with contractile parts of the muscle cells and they contain a heterogeneous population of vesicles: small spherical clear vesicles (44±2 nm), granules with fine-grained contents (135±5 nm), and a few spherical dense-core vesicles. The distance between the muscle cells is usually great — over 50 nm, but in the region of the sarcoplasmic processes the surface membranes come together to form a gap which in some areas does not exceed 10 nm.N. K. Kol'tsov Institute of Developmental Biology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 539–542, September–October, 1977. |
