Myelin (cells of NS) Flashcards
What is myelin?
Lipid rich sheath that wraps around axons
What is myelin made of?
70% lipid & 30% protein
Where does myelin come from?
- Oligodendrocytes in the CNS
- Schwann cells in the PNS
Where is myelin found?
- White matter tracts of the brain and spinal cord
- Peripheral nerves
- Not all axons are mylenated
What is the general function of myelin?
- To increase conduction velocity
What is the function of myelin protein?
- Maintain myelin structure
- Maintain integrity of axon-myelin interactions
In what sort of organisms is myelin present in?
- Not exclusive to mammals
- Myelin present in vertebrates & invertabrates
What is the evolution of myelin?
- Evolved in different species of the animal kingdom at different time points
- Shows different ways of myelination but achieve the same function
Necessary prerequisite to permit gigantism of gnathostome species (Jawed vertebrates that account for 99% of all living vertebrates)
What is the general principle of how myeling enwrapps an axon?
Oligodendrocytes send out multiple projections, known as MYELIN LAMELLAE - these wrap around multiple axons
What are myelin lamellae?
Formed by fusion of the apposed inner leaflets of the plasma membrane of oligodendrocyte projections
They are trapeziod shaped
Possibly watch back the slide about how myelin lamellae wrap axons
thanks
What are paranodal loops?
Noncompact myelin
What are dense lines in myelin?
(They appear darker)
Apposition of inner faces of the same lamella plasma membrane
What are interperiod lines in myelin?
(Thinner dark lines)
Apposition of outer faces of plasma membrane of subsequent wraps
Where are nodes of Ranvier found?
Between sections of myelin
