Disorders of CNS myelin Flashcards
What gives white matter its colour?
Myelin
What does white matter contain?
Axons
What gives white mater its insulative properties?
Rich lipid
Where is myelin present?
Central and peripheral nervous systems?
How is CNS myelin formed?
By oligodendrocytes
What does each CNS myelin cell form?
With a few exceptions, each cell forms myelinated internodes
What is CNS myelin’s major structural protein?
PLP/DM20
How is PNS myelin formed?
By Schwann cells
What does each PNS myelin cell form?
A single myelinated internode
What is PNS myelin’s major structural protein?
PO
What is saltuatory conduction?
‘Jumping’ between nodes of ranvier i.e. conduction between nodes
What does each oligodedrocyte have?
Several processes each of which maintains a myelin sheath often on different axons
What do Schwann cells form?
A single myelin sheath
What does the cytoplasm filled space allow?
Communication
What is a paranode?
Next to node of ranvier, where myelin sheath is anchored to the axon
What is a juxtaparanode?
In between internode and paranode
What does the myelinated CNS axon contain?
Microtubules, neurofilament and actin
What does the non-compact myelin contain?
Microtubules and actin
What does myelin sheath thickness correlate with?
Axonal diameter
What is G-ratio?
Axon diameter/fibre diameter
What is the G-ratio approx in humans?
0.6
What does a single oligodendrocyte produce?
5,000- 50,000 microns2 of myelin membrane surface area/day during development (Pfeiffer et al, 1993)
What is the approx length of a single oligodendrocyte?
10mm diameter
What happens to myelin composition in the absence of cholestrol?
Can not be made
What is the composition of myelin?
Cholestrol 27%
Glycosphingolipids 32%
Phospholipids 44%
What are the two major structural proteins in CNS myelin?
Myelin basic protein (MBP, approx 20%) Proteolipid protein (PLP, approx 50%)
What is the diameter of myelinated axons?
6 um
What is the diameter of unmyelinated axons?
500 um
What does increasing diameter do for conduction?
Increases conduction velocity
How does myelin accelerate conduction velocity?
Because sodium channels only at nodes at very high density
What is conduction speed for unmyelinated axons?
Slow