So many glia (questions)

Q1

Where there always glias cells to support nerve activity?

Q2

Nowadays glia have a multitude of functions, what was the original one?

Q3

Single origin with multiple loss vs. multiple origins.

Glia function … today

1. Structural support (protection)
2. Electrical/chemical isolation
3. Nutritive support (metabolic interaction)
4. Trophic support
5. Devellopment (growth)
6. Homeostasis
7. Modulation
8. Myelin (active)
9. Phagocytosis
10. Transmitter uptake
11. Inflammatory response

Glia/neuron-ratio through evolution

Glia/neuron-ratio through evolution

Tree of life

Glia phylogeny

Glia in development

1. Most of neuro-glia is derived from ectoderm
2. Nervous systems are subepidermal:
   • Vertebrates: Neurulation (folding)
   • Arthropods: Ingression (inward migration)
3. Glia provide guidance factors or follow neurons
4. Functional recruitment of cell types
   • Drosophila: Additional glia of mesectodermal origin (guidance factors; linking hemicords)

Function of the ur-glia

Extracellular homestasis and external trophic support

Requires extensive envelopment to stop diffusion.

Neuro-glia Gap-junctions

enable metabolic cooperation (but are rare today)

Structural support

Predatory glia-less flatworm

Microgila (phagocytosis in the nervous system)

Macrophages are present in early bilatiria

Myelin phylogeny