Peripheral Nerve

In the transverse section A cut or slice of the body or an organ for study., multiple circular axons are visible, each encased by a myelin sheathA fatty covering around axons that increases conduction speed., creating a distinctive ring-like appearance. The perineuriumA connective tissue sheath that surrounds a bundle (fascicle) of nerve fibers., a connective tissue layer, surrounds groups of axons, forming fasciclesBundles of nerve fibers within a nerve.
or
Bundles of nerve fibers within a muscle.. In the longitudinal section, nerve fibers appear as elongated, wavy structures running parallel to each other. Schwann cellsPNS glial cells that form the myelin sheath around peripheral nerve fibers. are present along the axons, and nodes of Ranvier, where the myelin sheath is interrupted, can be seen as small gaps along the fibers

Only the axons of these neuronsThe functional cells of the nervous system that transmit signals. are in the nerve. We name them “fibers” when we view them in a nerve.  So, a nerve is essentially bundles of little cylinders (axons).  These axons can be myelinate or not and they can be sensory or motor.  For example, the sciatic nerveThe largest nerve in the body, arising from the sacral plexus. carries motor information to muscles in your legs. It also collects sensory information from sensory receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter in your legs.  

The picture here shows a the cross section of a nerve.  On the outer, right side portion, you can see little circles, which are all myelinated axons cut transversely.  The circles have a dark pink outline that is the endoneuriumA thin layer of connective tissue surrounding each nerve fiber., wrapping each axon.  Inside the circle seems to be filled with tissue that does not take a stain and is a white color.  This is the myelin that does not like to take up this H&E stain.  However, if you inspect closely, you will see a faint pink dot. It is in the center of each of those white circles.  This is the axon itself.

Sweeping across the center of the nerve are axon cut in something like an oblique section.  The axons appear as faint pink lines instead of dots. You are almost able to see some nodes of Ranvier. The myelin is absent along the axon in these areas.