[The ultrastructure of the spines on serial sections of the rat cerebral cortex]

Electron microscopy was used for studying in detail the structure of dendritic spines of cortical neurons in layer III of the rat's sensomotor cortex. It is found that the electron-dense substance between the cisterns of the spine apparatus consists of orderly arranged fibrillae. Serial sections allowed to follow the changes in the spine apparatus, in the curvature and intermittent character of the synapse active zone, as well as the connection between the cisterns of the spine apparatus, and between these and other membrane structures of the spine. The correlation is shown between the dendrite diameter and the shape and size of the spine.