escribe the optic nerve, considering the following:
Is the nerve predominately myelinated or unmyelinated? How can you tell? Luxol fast blue is a dye that stains myelin sheath blue. Therefore, the nerves in image I and J are are predominately myelinated (blue) and only show small areas of demyelination (purple). Whereas, images K and L show extensive demyelinated areas (purple). Furthermore, in the demyelinating nerves where the myelin sheath is broken, lesions can be seen.
Is it myelinated by oligodendrocytes or Schwann cells? It is myelinated with oligodendrocytes because the optic nerve is part of the CNS. Furthermore, the images show the oligodendrocytes forming a myelin for several adjacent axons. Whereas, a Schwann cell would only be able to wrap around one axon, which is not seen in the images.
iii) Can you answer ii based on the data shown in this figure? If yes, explain. If no, describe a procedure you could use to determine this using light microscopy (hint: think IHC). No, LM and IHC staining could be used to view the oligodendrocytes IHC would label specific structure and components of the cross-section. Oligodendrocytes immunization could be identified when CD3-positive t-cells infiltrate the nerve parenchyma. From a LM we could see the densely arranged CD3 positive cells stained dark brown. An immunohistochemical marker can be used to view oligodendrocytes. Therefore, LM and IHC could be combined to create a single image.
iv) What is the approximate diameter of the optic nerve? 550 ?m, according to the 0.7cm scale on image L.
Q2: Is the optic nerve vulnerable to damage in peripheral myelinating diseases, such as Guillain-Barre syndrome? Why or why not? (2 marks) No the option nerve is not vulnerable to damage in peripheral myelinating diseases because it is located in the CNS. Guillain-Barre syndrome is only common in the PNS, where myelin sheath damage prevents the nerve from conducting electrical impulses normally.
Q3: Which (if any) ultrastructural feature(s) in these images indicate(s) whether the myelin is oligo-derived versus Schwann cell derived? (1 marks) The multiple layers oligodendrocytes wrapping around the axons forms the mylein sheath for many adjacent axons. Whereas, a Schwann cell would only be able to wrap around one axon, which is not seen in the images.

Q4: Describe the progression of myelin pathology in this animal model using the following terms (5 marks):
i) Axonal vacuole formation ii) Axonal condensation?iii) Loss of myelin compaction iv) Axonal degeneration v) Changes in length of the nodes of Ranvier

In the CNS the oligo cell interact with the axon and wrap around it in multiple layers of overlapping membrane (axonal condensation). Splitting of myelin sheaths could create a small package of cytoplasm adjacent to the axon (but separated by thin myelin sheath). This dense cytoplasm package contains axonal vacuoles. As the oligo wraps around the axon it provides electrical insulation to increase axonal conduction velocity. Furthermore, there is a loss of myelin compaction when the oligo wraps around the axon and major dense lines form. An axon degeneration can occur from a disease or injury, which leads to myelin sheath break down. The length of the nodes of Ranvier could vary in different class of axons. The length of nodes of ranvier could decrease to maximize conduction velocity of the axonal signal.

Q5: Describe the appearance of neurons and glia shown in each panel of the above Figure, and how this appearance was produced (i.e., via what techniques).
Panel A (IHC Staining): Oligodendrocyte (Glia) cells can be viewed as dense brown circles scattered across the field and the neurons are stained a light blue and also scattered across the field.
Panel B (CNPase staining): Less dense oligodendrocytes (brown and small circles) are scattered across the field. The neurons are stained a light blue and are also scattered across the field.
Panel C (H and E staining): Pyknotic neurons and glia are stained more blue (basophilic structures that bind to acidic/negatively charged structures) and the healthy neurones are stained more pink, with less blue dye (acidophilic or eosinophilic structures that bind to basic/positive charged structures). Both are scattered across the field.
Panel D (IHC staining): Oligodendrocyte (Glia) cells are dense brown aspects of the image, which are scattered across the field in and the neurons are stained a light blue. The glia are located near the neurons.
Panel E (IHC staining): Oligodendrocyte (Glia) cells are dense brown aspects of the image, which are scattered across the field in and the neurons are stained a light blue. The glia are located near the T-cell.

Q6: Define pkynosis, and describe the appearance of healthy neurons versus pyknotic neurons in the Figure. (2 marks)
Pkynosis is when a cell has a degenerative condition and the nucleus of a cell shrinks. This can be evident in staining. The healthy neurons stain more pink (acidophilic or eosinophilic structures that bind to basic/positive charged structures) and less blue. Whereas as the Pyknotic neurons stain more blue (basophilic structures that bind to acidic/negatively charged structures) because pkynosis is occurring.

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