Myelin and Myelination

Question 1

Myelin basic facts
Lipid-rich or not?
Role?
How are they synthesised?
increase of decrease conduction velocity?
Consequences of loss of myelin
surround all or some axons?

Answer 1

lipid rich
insulating sheath
non-neuronal cells
increase
profound neurological disorders which may alter memory and learning
some

Question 2

Where does myelin come from?
PNS

CNS

Does myelin stay with same axon in both PNS and CNS?

Answer 2

PNS - Schwann cells
they myelinate individual axons, surround all axons but may not myelinate all axons
stay with same axon

CNS - oligodendrocytes
- oligos myelinate several axons/ parts of axons

Question 3

myelins appearance?
linked external proteins?
linked internal proteins?
Made of?

Answer 3

protein-lipid-protein repeats
linked external proteins= intraperiod line(faint)
linked internal proteins= major period line(dense)
periodicity: PNS- 11.9nm, CNS- 10.7nm
(CNS more tighlty packed)
water- 40%, dry lipid- 70-80%, protein- 15-30%

Question 4

What is a cerebroside?
In genetically modified mice myelin forms but develops vacuoles… causes?
PNS and CNS differences? - cerebroside and sphingomyelin

Answer 4

dry lipid
Paralysis
PNS - less cerebroside and sulfatide
CNS - more sphingomyelin

Question 5

CNS myelin proteins: name 2 major ones

name problems

Answer 5

1)Myelin basic protein
=induces experimental allergic encephalomyelitis (model for multiple sclerosis)
- shiverer mice = die early
2)Proteolipid protein (PLP)
-natural problem with PLP is a mutation that causes ‘jumpy mouse’ (very little myelin, severe loss oligodendrocytes(in CNS), PLP produced is toxic)

Question 6

Other CNS myelin proteins (other than 2 main ones)

Answer 6

enzymes- cyclic nucleotide phosphodiesterase eg. proteases, lipid metabolism, carbonic onhydrase

Ig- like molecules (globular-like/ anitbody-like)
eg. MOG + MAG, oligo-axon communication

Question 7

PNS myelin proteins?

and defects?

Answer 7

Po - 50+% of PNS myelin protein
CMT 1b = Charcot-marie-tooth syndrome
PMP-22 - associated with CMT 1a

Adhesion molecule - compaction(compress layers)

Question 8

Multiple sclerosis(MS)
onset?
cause?
Genetics vs environment
autoimmunity?
therapy?

Answer 8

onset - 20-40s, relapsing or remitting, may be progressive
MRI shows plaques = areas of demyelination
periventricular white matter= vulnerable
MS= primary demyelination= ‘axon-sparing’

High incidence rate in caucasians, more woman than men, 30% c rate in MZ twins
viraly induced conditions could cause it eg. herpes
migration/geographic causes eg. Vitamin D idea

Autoimmunity = generally accepted, clear inflammatory response, no clear evidence for autoantigen, macrophage and protease activity degrades myelin

Therapy - steroids, interferons(interfere with immune response), immune suppressants, diet eg. vitamin D

Question 9

Gullen-Barre syndrome
What is it?
Cause?
treatment?

Answer 9

post viral/bacterial infection - harmful antibodies attack nerves
acute inflammatory response
primary demyelination
molecular mimicry?
treatment - intravenous immunoglobin- blood donation with healthy antibodies