University of Texas Medical Branch

Cell Biology Graduate Program

Organization of a peripheral nerve

Look at slide 3 in your class slide set.  The differential staining shows the different layers in peripheral nerve. Blue stain shows connective tissue.  Outside the nerve, loose connective tissue with adipose cells is called epineurium. The next layer of connective tissue which is denser and ensheaths different bundles of nerve fibers is called perineurium (shown dense blue in the slide). Delicate connective tissue surrounds each nerve fiber; this is called endoneurium.  In the photo and slide 3, you can see endoneurium around each fiber as delicate blue fibers.

The nerve fibers itself is stained purple/pink and is seen as a cylinder in the center of myelin which has a light orange stain.  In the above photo, the nerve fiber is labeled A (for axon) and the myelin is labeled m.  A Node of Ranvier can also be seen.  Find a comparable area in your slide 3.

After you have studied the layers in slide 3, use the above photograph to find the following:

• Node of Ranvier
• axon
• myelin sheath
• endoneurium.

Slide 10 shows a section through a peripheral nerve stained with Osmium tetroxide to bring out the myelin.

The myelin sheath is stained because of the abundance of lipids in the membranes wrapping around the axon.  Each myelinated axon looks like a donut.  You can also see adipose cells well in this section.  They contain stained, preserved fat droplets that stain dark brown-black.

Slide 40 is a peripheral nerve stained with Verhoeff's van Giesson stain. It shows nerve bundles called fasicles, epineurium, perineurium, endoneurium, axons and myelin. Practice your skills: find each of these structures and label the following figure.

Now, look at slide 25, which is a section of skin. You can find examples of peripheral nerves in the connective tissue.

The above view shows a cross section, which is easy to find after you completed the above exercises. However, a longitudinal section might be more challenging. Use the figure as a guide and find a longitudinal section. Ask your instructor for help. Hint: look for the same connective tissue capsule (perineurium) which contains a short section of a "wavy" bundle of nerve fibers.

(Note, eventually, you may have to distinguish it from bundles of smooth muscle.)