04 Glia Myelination

Question 1

Glia types (5)

Answer 1

5 types:

• Astrocytes
• Oligodendrocytes
• Schwann cells
• Microglia (soldiers)
• Ependymal cells

Question 2

Glia vs neurons: mitosis?

Answer 2

Glia: retain mitotic ability, but possible cancer
Neurons: no mitosis

Question 3

Astrocytes–types

Answer 3

1. Fibrous, in white matter

2. protoplasmic, in gray matter

Question 4

Astrocyte functions (8)

Answer 4

1. structural support, repair
2. K+ buffering–maintain neuron polarization
3. NT/metabolite removal (GLAST: glutamte-glutamine cycle)
4. contain NT receptors: can trigger Ca+ waves in astrocytes
5. BBB contribution, but not basis
6. Glial signaling–communication via gap jxns
7. Glial guides–neuronal migration during devo
8. stem cells–some astrocytes in adult can generate neurons/glia

Question 5

Oligodendrocyte functions (2),
myelination pattern

Answer 5

1. CNS myelination
2. Inhibits CNS axon growth/regeneration

1 oligodendrocyte can myelinate many axons.

Question 6

How do oligodendrocytes inhibit CNS axonal growth? list of 3

Answer 6

Proteins expressed that inhibit CNS axon growth:

1. MAG– myelin-associated glycoprotein
2. NI-35– Neurite inhibitor of 35 kDa: proteoglycan
3. Nogo gene

Question 7

Schwann cells myelination pattern

Answer 7

• 1 Schwann cell myelinates only 1 segment of 1 axon.

- 1 Schwann cell can surround many axons w/o myelination

Question 8

How do Schwann cells promote PNS axon growth?

Answer 8

growth promoting factors:

1. Laminin (required for PNS nerve regeneration)
2. Cell adhesion molecules (NgCAM/L1)
3. some Schwann cells secrete nerve growth factor

Question 9

Microglia functions

Answer 9

“Soldiers”:
-CNS macrophages–phagocytose CNS debris

• recruited in infection/seizure/injury.
• increase in # and size when neurons degenerate

Question 10

Ependymal cell functions

Answer 10

1. Modified Choroid plexus ependymal cells:
   - BBB basis–form tight jxns
   - produce CSF
2. Other ependymal cells:
   - line ventricles, no tight jxns
   - ciliary motion for CSF circulation

Question 11

Mesaxons CNS vs PNS

Answer 11

CNS: Only inner mesaxon

PNS: Both inner and outer mesaxons.

Question 12

MBP, MAG, MOG relation to disease?

Answer 12

1. Myelin basic protein
   - major CNS myelin structural protein, also present in PNS
   - basis of CNS autoimmune demyelinating diseases
2. Myelin-associated glycoprotein
   - inhibits CNS axon growth
3. Myelin-oligodendrocyte glycoprotein
   - surface of CNS myelin sheath
   - suspect antigen in autoimmune demyelinating diseases

Question 13

Nodes of Ranvier, CNS vs PNS

Answer 13

CNS: nodes are bare
PNS: nodes covered by Schwann cell cytoplasm

Question 14

In wrapped Schwann cells/Oligodendrocytes, how do nutrients from the cytoplasm of outer leaflet reach the inner leaflet?

Answer 14

PNS: Schmidt Lanterman incisures:
-‘tunnels’ of cytoplasm within major dense lines of Schwann cell

CNS: Longitudinal incisures

Question 15

Major vs minor dense lines

Answer 15

In oligodendrocytes or Schwann cells wrapping around axon:

• major lines are intracellular, compressed cytoplasm
• minor lines are opposed extracellular faces

Question 16

Conduction velocity: Myelinated vs unmyelinated

Answer 16

50x difference

Myelinated: 120 m/s
Unmyelinated: 2 m/s

Question 17

Autoimmune demyelinating diseases (2)

Answer 17

1. Multiple sclerosis
   - CNS only
   - chronic paralysis+sensory loss
   - MOG, MBP may be involved
2. Guillain Barre syndrome
   - PNS only
   - acute paralysis+sensory loss
   - usu starts with viral infection
   - usually recovery within few weeks
   - FDR may have had it instead of polio