Peripheral nerves usually contain axons from motor, sensory, and autonomic neurons that are mixed in bundles and organized into fascicles by connective tissue coverings. Schwann cells are the major glial cells of peripheral nerves. They surround and support unmyelinated nerve fibers (axons) and produce myelin sheaths that surround myelinated nerve fibers. Review the structure of myelin in the figure below and study the TEM images showing Schwann cells surrounding myelinated and unmyelinated axons. Osmium used in preparation of these specimens for TEM preserves the lipids of the myelin and stains them black, making it easy to see the many concentric layers of the sheath.

Gaps in the myelin sheaths between adjacent Schwann cells are called nodes of Ranvier. These nodes allow for saltatory conduction where nerve impulses or action potentials are able to rapidly move along the axon by jumping from node to node. Examine the images below and this preparation of isolated, teased-apart nerve fibers. Identify Schwann cell nuclei (SC) and nodes of Ranvier (arrows).

Next is more about peripheral nerves.