CNS Glial cells

Question 1

What are the different cell types in the CNS?

Answer 1

Question 2

What are the type of Glial cells involved in myelination?

Answer 2

One Oligodendrocyte:
- formed several myelin sheaths
- myelinated sections of several axons

One Schwann cell:
- forms one myelin sheath
- myelinated one section of an axon

Question 3

Astrocytes* What are the 2 classifications of astrocytes?

Answer 3

• Fibrous (white matter) —> arranged in rows between axon bundles
• Protoplasmic (grey matter)

Question 4

What is the role of Astrocytes in myelination?

Answer 4

Supports myelination by:
- aligning oligodendrocyte processes with axons
- releasing gliotrophic factors that promote oligodendrocyte survival
- increasing rate of myelin wrapping in response to electrical activity

Question 5

What are protoplasmic Astrocytes?

Answer 5

Fine processes that cover all areas of grey matter, including dendrites, axons, synapses, and vasculature

Question 6

What is the role of Astrocytes within the CNS?

Answer 6

1. Maintaining physiological homeostasis of CNS
   - K+ buffering and pH balancing
   - Re-cycling of neurotransmitters
   - alternative energy source
   - production of anti-oxidants
2. Formation and support of synaptic processes
   - Secrete synaptogenic factors to promote formation of synapses during development
   - Glypicans induce insertion of AMPA receptors of post-synaptic membranes
   - express glutamate transporters to remove glutamate from synapse, preventing excitotoxicity
   - AMPA-mediated Ca2+ signalling monitors neuronal activity, glutamate levels, promotes growth and synaptogenic signalling
3. Maintenance and formation of the BBB
   - astrocytes regulate cerebral blood flow and the permeability of the BBB
   - endfeet ensheath the brain vascular in a network called glial limitans

Question 7

What are Ependymal cells?

Answer 7

• derived from neuronal precursors (as Macroglia)
• forms single layer of ciliated cells that help to circulate CSF throughout ventricular system
• specialized ependymal cells form the choroid plexus —> responsible for the production of CSF in the body

Question 8

What are Microglia cells and their roles in the CNS?

Answer 8

• derived from yolk sac and bone marrow —> do not form neuroectoderm
• make up 7-10% of cells in CNS
• support neurogenesis, gliogenesis, differentiation, axonal synaptic pruning, myelination
• are resident immune cells, providing first line of defence —> release cytokines that have pro- or anti- inflammatory effects
• along with phagocytic cells, rapidly clear debris, protein, toxins, or dying cells within brain

Question 9

What are NG2 cells?

Answer 9

• act as markers making up 5% of CNS glia population
• referred to as polydendrocytes or oligodendrocyte precursor cells (OPCs
• retain proliferation into adulthood and can either remain as NG2 cells or differentiate into oligodendrocytes (and astrocytes)
• NG2 cells have synaptic connections with neurons (excitatory and inhibitory —> GABA) —> electrical activity from circuit may drive production of oligodendrocytes and promote myelination