Glia

Question 0

Glial cell types:

Answer 0

Astrocytes
Oligodendrocytes
Schwann cells
Microglia
Ependymal cells

Question 1

Glia:

Answer 1

Supporting elements of the CNS and PNS
Outnumber neurons, occupy only about 50% of CNS
no synapses & no action potentials

Question 2

Astorcytes are the _______ glial cells; most numerous; ___________ bodies; many long processes

Answer 2

largest; star-shaped

Question 3

What are the two types of astrocytes?

Answer 3

Fibrous astrocytes:
Have long thin processes and are found in white matter

Protoplasmic astrocytes:
Have shorter, thicker processes and are found in gray matter

**both have types of “end feet” or “foot processes”

Question 4

Oligodendrocytes:

Answer 4

Function: myelination of axons

one myelinated oligodendrocyte may myelinate many axons

Question 5

Functions of astrocytes:

Answer 5

1) Structural support and repair:
glial fibrillary proteins (GFAP), “connective tissue of the CNS”; surround synapses

2) Potassium spatial buffering:
neuronal membrane potential is maintained
not electrically excitable

3) Neurotransmitter and metabolite removal:
aid in rapid termination of the synaptic signal
GLAST takes up glutamate, converts glu to gln, then releases gln to neurons (glutamate-glutamine cycle)

4) Neurotransmitter receptors can trigger calcium waves inside cell
5) Contribute to the BBB
6) Gap junctions
7) Glial guides (neuronal migration)
8) Can serve as stem cells to generate neurons and glia

Question 6

____________ is a potent inhibitor of axon outgrowth and regeneration

Answer 6

central myelin

Question 7

Inhibitors of CNS axonal elongation:

Answer 7

1) Myelin associated glycoprotein (MAG)
2) Neurite inhibitor
3) Nogo gene & proteins

**All inhibit regeneration of CNS axons

Question 8

Myelin associated glycoprotein (MAG):

Answer 8

May be important in maintaining axon-myelin complexes (axon-glial signaling)
levels fall in mature PNS but not CNS

Question 9

Schwann cells

Answer 9

Counterpart of oligodendrocytes in the PNS

Function: myelination of axons in the PNS; only one segment of one axon

Surround all peripheral axons, whether myelinated or unmyelinated

Question 10

Schwann cells provide growth-promoting factors:

Answer 10

• Schwann cell basal lamina: laminin: required for regeneration of peripheral nerve
• Cell adhesion molecules: NgCAM/L1
• Some Schwann cells may secrete nerve growth factor

Question 11

Microglia:

Answer 11

• Function: phagocytosis (macrophage-like)
• Smallest; many short processes
• Increase in number (hyperplasia) and size (hypertrophy) when neurons undergo degeneration
• Recruited during infection, injury and seizure

Question 12

Ependymal cells:

Answer 12

• Cuboidal or columnar epithelial layer lining the inside of the neural tube
• Some are ciliated or have microvilli
• Ependymal cells lining the ventricles have desmosomal junctions; some substances in CSF can penetrate the brain (no tight junctions)
• modified ependymal cells and associated capillaries form the choroid plexus; since they have tight junctions they also form the CSF/brain barrier

Question 13

Functions of ependymal cells:

Answer 13

• barrier b/w brain and CSF
• CSF circulation
• produce CSF (choroid plexus)

Question 14

Myelination:

Answer 14

• In the PNS: 1 Schwann cell myelinates 1 segment of 1 axon

* In the CNS: 1 oligodendrocyte myelinates many axons

Question 16

Myelin structure

Answer 16

• Inner mesaxon: present in both CNS and PNS
• Outer mesaxon: present only in PNS
• Major dense lines
• Minor dense lines
• Axons > 1 µm in diameter are myelinated
• High in lipid content
• Thickness increases with axon diameter

Question 17

Myelin proteins:

Answer 17

1) Myelin basic protein (MBP)
2) Myelin-associated glycoprotein (MAG)
3) Myelin-oligodendrocyte glycoprotein (MOG)

Question 18

Myelin basic protein (MBP):

Answer 18

• Major structural proteins in CNS & PNS
• On the cytoplasmic face of the myelin membrane
• Basis for CNS autoimmune disease

Question 19

Myelin-associated glycoprotein (MAG):

Answer 19

In both CNS and PNS

Question 20

Myelin-oligodendrocyte glycoprotein (MOG):

Answer 20

• CNS only
• On surface of myelin sheath and oligodendrocytes
• Target antigen in autoimmune aspects of CNS demyelinating diseases

Question 21

Nodes of Ranvier:

Answer 21

• Axolemma exposed to ECF
• Saltatory (“jumping”) conduction
• High concentration of voltage-gated Na channels
• Internode size is directly proportional to axon size
• PNS: covered by the Schwann cell cytoplasm
• CNS: nodes are bare

Question 22

Clefts (incisures):

Answer 22

Function: cytoplasmic nutrients to inner leaflets

• PNS: Schmidt-Lanterman incisures
• CNS: Longitudinal incisures

Question 23

__________ axons in the ___________ are surrounded by __________ cytoplasm and ___________.

Answer 23

Unmyelinated; PNS; Schwann cell; basal lamina

Question 24

Myelin function:

Answer 24

a. Insulation: decreases ionic flux across the axolemma; conserves cellular ATP.
b. In myelinated axons: Saltatory conduction. Conduction velocity can reach up to 120 m/sec.
c. In unmyelinated axons: action potentials pass continuously along the axolemma, causing the conduction velocity to be < 2 m/sec.

Question 25

Demyelinating diseases

Answer 25

1) Multiple Sclerosis

2) Guillain-Barré Syndrome

Question 26

Multiple Sclerosis

Answer 26

• A chronic, demyelinating disease of the CNS.
• May be autoimmune disease with genetic and environmental risk factors.
• One consequence of demyelination is scarring (gliosis or sclerosis) throughout the CNS.
• Abnormal and slowed conduction of action potential leads to paralysis, other symptoms.
• Disruption of the blood brain barrier and acute inflammation.
• Usually marked by periods of remission and relapses over many years.
• Affects both sensory and motor axons, leading to sensory and motor deficits.

Question 27

Guillain-Barré Syndrome

Answer 27

• Acute, inflammatory demyelinating disease of the PNS.
• Attacks myelin of the peripheral nerves that innervate muscles and skin.
• Autoimmune disease against one’s own myelin proteins.
• Demyelination leads to slower and abnormal conduction of action potentials.
• Difficulty with both sensory perception and motor coordination.

Question 28

________________ is a demylelinating disease that usually presents as a viral infection

Answer 28

Guillain-Barré Syndrome