Myelin and Myelination Flashcards
Myelin
- Lipid-rich
- Synthesised by non-neuronal cell
- Increases conduction velocity
- Loss of myelin produces neurological disorders
- Myelin may alter in learning and memory
What percentage of dry weight of white matter is myelin?
50%
Where does myelin come from in the PNS?
Schwann cells
Where does myelin come from in the CNS?
Oligodendrocytes
Schwann cells myelinate _____ axons
Individual
Oligos myelinate ______ axons/parts of axons
Several
What does myelin look like?
Protein - lipid - protein repeats
What is the periodicity of myelin in the PNS?
11.9 nm
What is the periodicity of myelin in the CNS?
10.7 nm
What percentage of myelin is water?
~40%
What percentage of myelin is dry lipid?
70-85%
What percentage of myelin is protein?
15-30%
What is myelin made of?
- Water
- Dry lipid
- Protein
PNS has less…
- Cerebroside
- Sulfatide
CNS has more…
Sphingomyelin
CNS myelin proteins
- Myelin basic protein (MBP)
- Proteolipid protein (PLP)
Proteolipid protein (PLP)
- Important role in formation or maintenance of myelin
- Mutation causes Jimpy mouse
Myelin basic protein (MBP)
- Important in myelination of nerves
- Induces experimental allergic encephalomyelitis (EAE)
- Implicated in MS
Other CNS myelin proteins
Enzymes
- Cyclic nucleotide phosphodiesterase
- Proteases
- Lipid metabolism
- Carbonic anhydrase
Ig-like molecules
- MOG and MAG
- Oligo-axon communication
PNS myelin proteins
- P0
- MBP
- PMP-22
P0
50+% of PNS myelin
MBP in PNS
Less important than in CNS
PMP-22
Alterations in gene expression associated with Charcot-Marie-Tooth 1a?
Multiple Sclerosis
- Onset 20s - 40s
- Variable severity
- May be progressive
- Plaques shown in MRI
- Primary demyelination
What type of white matter is vulnerable in MS?
Periventricular white matter
What is the percentage concordance of monozygotic twins with MS?
30%
What causes MS?
- Geographic distribution suggests environment, vitamin D
- Virally - herpes virus
What race is MS more common in?
Caucasians
What type of disease is MS?
Auto-immune
No clear evidence for particular auto-antigen
What degrades myelin in MS?
Macrophage and protease activity
Therapy for MS
- Steroids
- Interferons
- Cyclophosphamide, antibodies (immune su-pressants)
- Haemopoietic stem cells
- Vitamin D
Guillan-Barre Syndrome
- Post viral/bacterial infection
- Acute inflammatory response
- Primary demyelination
- LPS of bacterial cell coat and myelin lipids/proteins molecular mimicry
Guillan-Barre Syndrome symptoms
- Numbness
- Pain
- Muscle weakness
- Balance/coordination problems
- Pins and needles
Guillan-Barre Syndrome treatment
- IV immunoglobulin
- Plasma exchange - plasmapheresis
Multiple sclerosis symptoms
- Fatigue
- Vision problems
- Numbness/tingling
- Mobility problems
- Sexual problems
- Problems with thinking, learning and planning
