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chronic inflammatory demyelinating polyneuropathy
where are NT in a cell located?
the conducting fiber
myelin used for?
speeding transmission of signal
what percentage of dry mass are lipids?
excitatory and inhibitory NT?
- glutamate (excite)
- GABA (inhibit)
what arthropoda has it?
- crustacea (shrimps)
- annelida (earthworms)
is it thicker in CNS or PNS?
jawed vertebrate includes reptiles, aves (finches), mammals, amphibian, osteichthyes (trouts), chondrichythyes (sharks and rays)
what does loss of myelin cause?
slowing of conduction by interrupting localized current flow
where are sodium channels located
at nodes of rangier
why are myelinated axons faster in electrical transmission?
action potential at one point along unmyelinated axon produces current that only propagates short distance
how does myelination reduce electrical transmission
myelin reduces effective conductance and capacitance of internal axolemma
cell membrane surrounding an axon
as schwann cells wrap around axon, what happens to its organelles
squeezed to the outside
repeating of action potential down the axon
glial axonal junctions
junction between glial and axon membrane (points of contact)
- small pockets of cytoplasm left behind during the Schwann cell myelination process
- create communication channels between outer layer and inner layer
- white space is greater in PNS than in CNS
- white is residual cytoplasm
interlamellar tight junctions (radial component)
firm adhesion between membranes in the internode and as permeability barrier
difference between PNS and CNS sheaths
- PNS: sheaths are separated by collagen (SC outside sheath)
- CNS: sheaths are almost continuous looking
major dense lines
- formed by cytoplasmic faces of the plasma membrane
- dark in electron micrographs, b/c osium metal is dense, binds to cytoplasm
cytoplasm forms the major dense lines and the two external surfaces form the myelin intraperiod lines
major proteins in CNS and PNS
- CNS (PLP) multipass
- PNS (P0) single pass
where is myelin basic protein located (MBP) and what are its characteristics?
- in cytoplasm
- easily dissociated from membrane
difference between schwann and oligodendrocytes
one oligodendrocytes form many myelin sheaths (may be not next to each other)
why do multiple sclerosis occur?
b/c immune cells attack the antigens on oligodendrocytes
keep getting made
myelin not compacted correctly, poor contact between myelin surfaces
myelin targeted then other structures go with it
neurons dies first, then myelin destroyed
where cell bodies are
where nerve fiber is crushed or cut, in which part of the axon separated from the neuron's cell body degenerates distal to the injury
what are acquired disorders?
guillain barre and CIDP (chronic form of guillain barre)
- experimental form in mice that mimics MS
- EAN (mimic Guillian Barre)
PLP, P0, PMP22, Cx32
how does inflammation cause demyelination?
cytokine overproduction via the up regulation of tumor necrosis factor or interferon
compact myelin where?
schwann cell microvilli
at node of Ranvier
glial axonal junction located where?
voltage gated K channels where
- first appear at nodes, then move to paranode and then juxtaparanode
- important for dampening excitability (only mature fibers conduct fast enough to make them unneeded)
voltage gated Na+2 where?
what does K channels in mature juxtaparanodes functionally may do?
protect fibers in case of partial de-myelination
how can lipids be separated from other proteins?
protein be separated?
dissolve membrane by digesting it
what is one why to measure myelin metabolism?
what is isolated myelin
- separated b/c of high lipid content
- myelin will float higher in sucrose gradient
- internodal, compact myelin
- simple composition, few proteins
- (you ignore junction myelin b/c they are more protein rich)
what kind of proteins does myelin at junction have?
- contactin (gap junction)
- CAMs proteins (cell adhesion molecule)
link loop to axolemma in paranode
- link terminal loops together
- adheren junction (occur at cell cell in epithelial tissues)
- node elongation with loss of NF155 may allow extracellular current flow to juxtaparanode
- may cause redistribution of Kv1, Na voltage and Caspr
- myelin retraction
- paranodal loop eversion (flip inside out)