SOME FEATURES OF THE SUBMICROSCOPIC MORPHOLOGY OF SYNAPSES IN FROG AND EARTHWORM

TLDR

Electron micrographs of synaptic regions in frog sympathetic ganglia and earthworm nerve cord neuropile are presented. Synaptic membranes are 70–100 Å thick with a 100–150 Å intermembranal space, and presynaptic vesicles (200–500 Å) lie close to the membrane; in earthworm neuropile elongated vesicles traverse membrane gaps, while mitochondria and a short filamentary component are nearby.

Abstract

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.