Peripheral nerve

Although myelinated axons in the PNS are usually larger than unmyelinated axons, they can vary greatly in their diameters.  In general, larger axons have thicker myelin sheaths.  Here, the myelin is visible as dark bands surrounding each axon.  PNS myelin is produced by Schwann cells, which associate with a single axon and produce a single internode of myelin.

Unmyelinated axons are generally less than one micron in diameter.  Numerous unmyelinated axons associate with a single Schwann cell, each lying in a longitudinal indentation of the Schwann cell surface.

These images compare the structure of a small peripheral nerve at the light (left, toluidine blue stain) and electron microscopic (right) levels.  These peripheral nerves contain a mixture of myelinated and unmyelinated axons.  Both nerves are located in dense irregular connective and a distinct perineurium demarcates the nerves from the surrounding connective tissue.  1000x, 1500x

These images compare the structure of a small peripheral nerve at the light (left, toluidine blue stain) and electron microscopic (right) levels.  These peripheral nerves contain a mixture of myelinated and unmyelinated axons.  Both nerves are located in dense irregular connective and a distinct perineurium demarcates the nerves from the surrounding connective tissue.  1000x, 1500x

These images compare the structure of a small peripheral nerve at the light (left, toluidine blue stain) and electron microscopic (right) levels.  These peripheral nerves contain a mixture of myelinated and unmyelinated axons.  Both nerves are located in dense irregular connective and a distinct perineurium demarcates the nerves from the surrounding connective tissue.  1000x, 1500x