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Medical Neuroscience Block 1 > 3 - Glia and Myelination > Flashcards

3 - Glia and Myelination Flashcards

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USMLE® Step 1 flashcards
1
Q

What are glial cells? What is their structure?

A

Supporting elements of the CNS and PNS that occupy ~50% CNS volume.

Have processes by no synapses and no action potential.

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2
Q

What is a result of glial cells retaining their mitotic ability into adult life?

A

Formation of scars (gliosis), and that the majority of CNA cancers are of glial origin.

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3
Q

What are the five major classes of glia?

A
  1. Oligodendricytes - means cells with few dendrites
  2. Schwann cells
  3. Microglia
  4. Ependymal cells - line vessels
  5. Astrocytes
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4
Q

What are the characteristics of astrocytes? What are the two types?

A

Largest type of glia, and most numerous.

Two types: fibrous and protoplasmic.

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5
Q

What is the difference between fibrous and protoplasmic astrocytes? What is similar?

A

Fibrous: long, thin processes in white matter.

Protoplasmic: shorter, thicker processes in gray matter

Both have processes that butt up against blood vessels ,called end feet, where metabolites exchange (forms part of lymphatic system)

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6
Q

What major protein is found in astrocytes? What is its function?

A

GFAP: connective tissue of CNS that fills spaces and surrounds synapses.

Responsible for gliosis or sclerosis (glial scare)

Can engulf degenerated neuronal debris.

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7
Q

What is the function of K+ spatial buffering done by astrocytes?

A

It takes up excess excess K+ released by neurons to help maintain the neuronal membrane potential.

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8
Q

Astrocytes have GLAST, what is this?

A

Glutamate-glutamine cycle:
They take up glutamate and convert it to glutamine so it can be taken up by neurons and made back into glutamate.

Don’t b/c glutamate is cytotoxic.

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9
Q

______ contribute to, but are not thought to be the basis for the BBB and also help neurons mitigate their terminal destination.

A

Astrocytes.

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10
Q

What are the characteristics of oligodendrocytes and what are the type types?

A

Smaller than astrocytes, fewer processes, round nuclei.

Types:

  1. Perineural oligodendrocytes (satellite cells)
  2. Oligodendrocytes in white matter
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11
Q

What is the function of oligodendrocytes? What does this inhibit and is it good or bad?

A

CNA myelination: one oligodendrocyte usually myelinates many axons.

Central myelin is a potent inhibitor of axon outgrowth and regeneration.

This is good because you don’t want out of control axonal growth under normal circumstances.

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12
Q

What are inhibitors of CNS axonal elongation that are expressed in oligodendrocytes?

A

Myelin-associated glycoprotein (MAG), neurite inhibitor, and Nogo gene and proteins.

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13
Q

What is the function of Schwann cells?

A

PNS myelination: 1 schwann cell myelinates only 1 SEGMENT of 1 axon.

1 PNS axon can be myelinated by 50-500 Schwann cells.

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14
Q

What are the three growth-promoting factors that Schwann cells provide?

A
  1. Basal lamina - important for regeneration
  2. Cell adhesion molecules (NgCAM/L1)
  3. Some may secrete nerve growth factor
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15
Q

Peripheral nerve regeneration requires _____?

A

laminin

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16
Q

Schwann cells surround both _______ and ______ axons.

A

Myelinated and unmyelinated

17
Q

What is the structure of microglia? What happens to them as neurons degenerate?

A

Smallest glial type with many short processes.

Increase in number (hyperplasia) and size (hypertrophy) when neurons age.

18
Q

When are microglia recruited/activated?

A

Recruited during infection, injury, and seizure.

May be activated in MS, parkinsons, alzheimers, and AIDs related dementia.

19
Q

What is the primary function of microglia?

A

Phagocytose debris in the CNS.

20
Q

What are the function of ependymal cells?

A
  1. Provide some barrier between brain and CSF
  2. Ciliary motion helps CSF circulation and microvilli for absorption of CSF
  3. In choroid plexus, produce CSF
21
Q

What is the structure of ependymal cells? Where are they typically found?

A

Cuboidal or columnar epithelial cells that line cerebral ventricles and central canal.

May have cilia or microvilli.

Desmosomal junctions allows some substances in CSF to get to the brain

22
Q

Describe the ependymal cells of the choroid plexus?

A

Form tight junctions, which are the basis of the CSF/brain barrier.

23
Q

What cells are responsible for myelination in the PNS? What about in the CNS?

A

PNS: Schwann cells

CNS: Oligodendrocytes

24
Q

What is the difference between myelination in the PNS and CNS (besides the fact that different cells types do it)?

A

PNS: myelin has both inner and outer mesaxons

CNS: myelin has NO outer mesaxon (because it is off to form some other axon)

25
Q

What are major dense lines and minor dense lines (intraperiod lines) found in myelinated (PNS) axons?

A

Major dense lines: apposed cytoplasmic faces

Minor dense lines: apposed extracellular faces

26
Q

What is myelin made out of?

A

80% fat, 20% protein

27
Q

What are the three types of proteins found in myelin? Which are found in PNS vs. CNS?

A
  1. Myelin basic protein (MBP) - in both PNS and CNS
  2. Myelin associated glycoprotein - in both PNS and CNS
  3. Myelin-oligodendrocyte glycoprotein (MOG) - CNS only
28
Q

What is the function of myelin basic protein (MBP)? Where is it found and what it it the bases for?

A

Major structural protein of CNS (also present in PNS).

On cytoplasmic face of myelin membrane.

Basis for autoimmune disease: experimental allergic encephalomyelitis

29
Q

Where is myelin-oligodendrocyte glycoprotein (MOG) found? What is it implicated in?

A

On surface of myelin sheath and oligodendrocytes.

Implicated as a target in autoimmune aspect of CNS demyelinating diseases.

30
Q

What is the function of nodes of Renvier? What is located there?

A

Axolemma exposed to EC fluid allows saltatory conduction from node to node.

High concentration of voltage gated Na+ channels so ions can flow across membrane.

31
Q

What is the difference between the Nodes of Ranvier in the CNS and PNS?

A

PNS: Nodes covered by Schwann cell cytoplasm and basal lamina.

CNS: nodes are bare because the CNS has the skull for protection

32
Q

What are Schmidt Lanterman Clefts/Incisures and where are they found?

A

“Split” in major dense lines filled with Schwann cell cytoplasm that serves to provide cytoplasmic nutrients to the inner leaflets.

Found in PNS.

33
Q

What are Schmidt-Lantermal Incisures called when they are found in the CNS?

A

Longitudinal incisures.

34
Q

What is the function of myelin?

A

Provides insulation, reduces ionic flux across the axolemma, and conserves cellular ATP.

35
Q

How do action potentials travel through unmyelinated axons? How fast is this compared to myelinated axons?

A

They pass continuously along the axolemma with a conduction velocity <2 m/sec

Myelinated velocity can reach 120 m/sec

36
Q

What are the characteristics of multiple sclerosis? What are some possible causes?

A
  • Chronic* demyelinating disease of the CNS with several myelin antigens that may be involved.
  • sclerosis (scarring) and abnormal and slowed conduction of APs.

Affects both sensory and motor axons, may lead to paralysis.

Periods of remission and replase over yeasr.

May be autoimmune disease

37
Q

What are the characteristics of Guillain-Barre Syndrome? What is the cause?

A
  • Acute* inflamm. demyelinating of nerves in the PNS that innervate muscles and skin.
  • slowed conduction of APS
  • difficulty with sensory perception and motor coordination

Autoimmune against one’s own myelin proteins (PO)

Ascending symptoms starting with lower extremity, and descending relief of symptoms.

Medical Neuroscience Block 1 (10 decks)

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