Histology Dissection Lab

 Nervous System Histology and Dissection Lab

Peripheral Nerve Histology (Microanatomy)

The differential staining in Slide 1 shows the different layers in peripheral nerve. Connective tissue stains blue. Outside the nerve, loose connective tissue combined with adipose cells is called epineurium. The next layer of connective tissue, denser and ensheathing different bundles of nerve fibers is called perineurium (dark Purplish-­blue in the slide). Delicate connective tissue called endoneurium surrounds each nerve fiber and appears as delicate blue fibers. The nerve fiber itself stains pink and is seen as a cylinder in the center of myelin with a lighter pink stain. The nerve fiber is labeled A (for axon) and the myelin is labeled M. A Node of Ranvier (R) is also visible.

1. Western science developed using Latin as the language root for terminology to create classification systems. Using just the three terms in bold in the paragraph above, we see a prefix of epi-, peri-, and endo- used to describe the structural elements in the slide of a nerve fiber. This coding system is helpful and consistent to describe the intricate structures of anatomy so that scientists, healthcare professionals and students can have a common naming convention and simplify complexities by establishing or seeing patterns. In this slide, the "epineurium" denotes the uppermost or outermost layer resting "upon" the other layers; the "perineurium" term--which means around--is used to describe the tissue that surrounds each nerve fiber, and "endoneurium," which uses the Latin prefix of "endo" means "within" or "inside," so we can clearly learn that something labeled as "endoneurium" is referring to the interior portion of a structure. 

2. Looking at the way that nervous tissue and muscle tissue is bundled, we can say that muscle fibers are ensheathed into fascicles like the strands of twine may be bound to create a rope or cable--except the fibers are sheathed without the braiding quality we can see in ropes and cables. One can also imagine that each fascicle contains strands of muscle fibers similar to the box of spaghetti pasta noodles. The fascicles provide a structural support that protects from injury and actually contributes to the movement process.

Nerve tissues are bundled, though their structure differs considerably from muscle tissues. Nerve tissues or "axons" are bundled in a myelin sheath that enables swift relay of electrical impulses to muscle tissues. Acting like an insulator, bio-electrical impulses can travel efficiently with this shield, thus saving the body's energy by not needing the active transport process (ATP) to do their work. 

3. The dark blue and purplish ares on the slide are the perineurium or the connective tissue that is around the nerve fibers.

 

 A. Node of Ranvier, indicated on the slide above by white gaps in intervals in between Schwann cells along an axon; these are unmyelinated spaces, that is, not covered by the insulating sheath., where the axon is exposed.

  B. Axon- represented by the deeper mauve pink with an elongated smooth appearance are the section of the neurons which carry electrical impulses, or bio-electric messages to the terminals where they inform muscles cells.

  C. Myelin Sheath is represented by the textured pink boundaries to either side of the axons described above. This sheath is generated by the Schwann cells along the axon.

  D. Endoneurium is the structure that is represented by blue fibers in the diagram above. The  endoneurium is the loosely connective tissue matrix that holds the neurons and blood vessels in formation inside the myelin sheath.  

Slide 3 Question:
To diagnose a nerve disease, what could the lipids tell you?

The lipids stained by the dye indicate health of the myelin sheath that can be damaged. If  a view of these lipids show deformities, gaps where the insulating blanket doesn't quite cover the neurons, this could indicate onset of multiple sclerosis.

Fasicles shown in diagram to left are like the casing on a sausage, holding the neurons in packages.

Perineurium represents the white boundary zones which have a denser quality that the interior tissues.

Endoneurium, which refers to what is inside, is what surrounds the neurons-the loose matrix located inside the fasicles.

Axons are the superhighway lane that is labeled on the above diagram.

Myelin Sheath, labeled above, is again what protective barrier the Schwann cells produce to increase the speed of electrical impulses.