[Synapses with myelinated and unmyelinated preterminal portions of axons in cat cerebral cortex].

The electron microscopic study of the cat cerebral cortex revealed two kinds of preterminal axonal regions with synaptic boutons at the end: nonmyelinated and myelinated. In the first case their diameter was about 90 nm; in the second case it was considerably greater; the myelin could reach the bouton. The possible physiological meaning of these structural features is discussed.