They are normally present only in small numbers in the adult CNS, but proliferate and become activtly phagocytic in region of injury and disease. These are the smallest of the glial cells, and have short twisted processes. Like oligodendrocytes, the Schwann cells turns about the axon several times, wrapping it in concentric layers of membrane. Unlike oligodendrocytes, each Schwann cell wraps around a single axon and provides the myelinated region between two nodes of Ranvier. You will see myelinated peripheral axons in today's laboratory.
All cortex is laminated, meaning that it consists of distinct layers when seen under a microscope.
The images to the left are electron micrographs of the human neocortex showing the arrangement of nerve-cells in two different cortical regions. The roman numerals designate the different layers that are present. If you have trouble seeing the layers, squint at the images. Note the external layer that has few or no cells. Note the middle layers that have larger looking cells.