Nervous Tissue 3: Nerve fibre & covering Flashcards
Axon is covered by —- and contains ——
- Axolemma
- Axoplasm
Site of Unmyelinated nerve fiber without Schwan cells
Grey matter
Site of unmyelinated nerve fiber with Schwan cells
Sympathetic post-ganglionic fibers
Site of myelinated nerve fiber with Schwan cells
Peripheral Nerve fibers
Site of myelinated nerve fiber without Schwan cells
White matter
Difference between central nervous system & peripheral Nervous system in formation of myelin sheath
- In Peripheral NS: Myelin sheath is formed from schwann cells, with each schwann cell wraping around 1 segment of axon
- In CNS: Myelin sheath is fromed from oligodendroglia, with each oligodendroglia wraping around 1 or more segments of multiple axons
True or false, Schwann cells exist in CNS (white matter & grey matter)
false
Stain for Myelin sheath
Osmic Acid (stains black)
Describe histology of myelin sheath
- cell membrane Made of higher lipid proprtions than other cells
- LM: dissolves under H/E, so stained with osmic acid
- EM: Shows nodes of ranvier (spaces between adjacent sheath cells) & Internodal segments (Segments of the sheath)
Function of Myelin sheath
Enhances speed of nerve impulses (sultatory conduction)
Describe the formation of myelin sheath
- Axon invaginates into near sheath cell (Schwann cells or oligodendroglia) & becomes surroounded by single turn of cell membrane
- Single turn progresses into **many turns **
- intervening cytoplasm is pushed to cell body causing compaction
- Fusion of cell membranes of the spirally arranged turns
When it comes to the peripheral NS, inside the bundle, nerve fibers are connected by
Endoneurium (sheath of henle)
When it comes to the peripheral NS, Nerve bundles are surrounded by
Perineurium
Dense connective tissue surrounding peripheral nerve is called
Epineurium
Perineurium is formed of
flattened epithelial like cells joined by tight junctions
