Lecture 6 Flashcards

1
Q

What are two structural characteristics of myelin?

A
  1. lipid-rich, living insulating sheath

2. 50% dry weight of white matter

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2
Q

Where is myelin synthesized?

A

non-neuronal cells

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3
Q

Can myelin distribution change in learning and memory?

A

yes

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4
Q

Myelin surrounds some axons. Why?

A

High metabolic energy needed to produce myelin

Highly selective when wrapping around axon

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5
Q

What does myelin look like?

A

Dense staining wrapped around peripheral axon
Myelin gives white color to the white matter in the brain
Multi-layered membrane tightly wrapped and has light and dark lines

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6
Q

What is are differences between myelin wrapping between Schwann cells and oligodendrocytes?

A
Schwann: 
myelinates individual axons
Cell is flattened out - flattened cytosol
tubukar edge
Oligodendrocytes: 
myelinates several axons or several parts of axons
cell body is separate
bumpy cytosol
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7
Q

What does compaction of the membranes contribute to?

A

Allows proteins to crosslink with each other

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8
Q

What does a dense line do?

A

Compresses together

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9
Q

What is periodicity?

A

Distance between lines composition of myelin is different between PNS and CNS

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10
Q

Why does myelin look like what it does?

A
  • protein-lipid-protein repeats
  • linked external proteins = intraperiod line (faint)
  • linked internal proteins = major period (dense) line
  • Periodicity
    PNS: 11.9 nm
    CNS: 10.7 nm
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11
Q

What is myelin composed of and at what proportions?

A

40% water
70-85% dry lipid
15-30% protein

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12
Q

What are the dry protein and dry lipid compositions in myelin, white matter and gray matter?

A
Myelin:
30% protein 70% lipid
White matter:
39% protein 55% lipid
Gray matter:
55% protein 33% lipid
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13
Q

What are the cholesterol, cerebrosides, galactolipid, plasmalogens, phospholipid compositions in lipid in myelin, white matter and gray matter?

A

Myelin:
28% cholesterol 23% cerebrosides 28% galactolipids 12% plasmalogens 43% phospholipids
White matter:
28% cholesterol 20% cerebrosides 29% galactolipids 11% plasmalogens 46% phospholipids
Gray matter
22% cholesterol 5% cerebrosides 7% galactolipids 9% plasmalogens 70% phospholipids

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14
Q

Which does myelin compositions more closely resemble; white matter or gray matter?

A

White matter

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15
Q

What happens when cerebrosides are lacking?

A

Myelin forms but develops vacuoles

Paralysis is seen in aged knockout mice because myelin starts to delaminate

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16
Q

When comparing between PNS and CNS, PNS has less _ and _ while CNS has more _.

A

cerebroside
sufatide
sphingomyelin

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17
Q

What are two major myelin proteins?

A
myelin basic protein (MBP)
proteolipid protein (PLP)
18
Q

What does a natural mutation of proteolipid protein lead to?

A
Jimpy mouse: "jerky" motor disturbance
Very little myelin
Die early
Severe loss of oligos
PLP produced is toxic
19
Q

What is a milder knockout mouse of jimpy mouse?

A

Rumpshaker

no PLP toxicity

20
Q

What does Myelin Basic Protein (MBP) induce and what can it be a model for?

A

Induces experimental allergic encephalomyelitis (EAE)

model for MS

21
Q

What is a condition found when MBP is lacking?

A

shiverer mouse

22
Q

What are enzymes found in myelin?

A

Cyclic nucleotide phosphodiesterase
Proteases
Lipid metabolism
Carbonic anhydrase

23
Q

What do Ig like molecules contain?

A

Immunoglobin domain

24
Q

What are Ig-like molecules found in myelin? What do they allow?

A

MOG and MAG

Oligo-axon communication

25
How much do PNS myelin protein take up in the PNS myelin? What is a major protein?
over 50% | P0
26
What happens when the PNS myelin protein is being knocked out?
Condition: Some Charcot-Marie-Tooth syndrome (CMT 1b) Profound myelin defects adhesion molecule compaction
27
PMP-22 is a PNS myelin protein. What gene produces it?
CMT 1a
28
What happens when CMT 1a is mutated?
Lethal | Tubular loop structure separate too much and widen the node of Ranvier
29
What is the onset age range for MS?
20s to 40s
30
What is vulnerable in MS patients?
Periventricular white matter
31
What is an example of axon demyelination?
axon-sparring
32
Where does demyelination occur in MS?
CNS
33
What is the female to male ratio in caucasians with MS?
1.5:1
34
What have linkage studies shown in MS?
Immunological factors involved
35
What do clusters/migration/geographic distribution suggest?
Environment | Vitamin D involvement
36
What virus can induce MS?
herpes
37
What activity degrades myelin in MS?
macrophage and protease
38
Name five types of therapies for MS?
1. steroids 2. interferons - interferes with immune system 3. other immune suppressants 4. hemopoietic stem cells 5. dietary
39
Name examples of immune suppressants for MS?
cyclophosphamide antibodies e.g. alemtuzumab
40
What is a dietary factor in MS?
Vitamin D intake
41
What kind of infections can lead to Guillan-Barre syndrome?
Post viral/bacterial infections | e.g. campylobacter jejuni, zika virus (?)
42
What are symptoms if Guillan-Barre Syndrome?
Acute inflammatory response Primary demyelination Molecular mimicry e.g. Between LPS of bacterial coat and myelin lipids/proteins