Glial Cells in CNS

Study Notes

Glial cells communicate with neurons and among themselves through chemical signals.
They support neurons physically and metabolically.
They maintain the optimal composition of the extracellular environment surrounding neurons.
They actively modulate synaptic function and are crucial for learning and memory.

There are four major types of glial cells in the CNS: astrocytes, oligodendrocytes, microglia, and ependymal cells.
Each type has specific roles.

Microglia are the immune defense cells of the CNS.
They are similar to monocytes and derived from bone-marrow tissue.
They migrate to the CNS during embryonic development and remain stationary until activated.
In the resting state, they release low levels of growth factors to support neurons and glial cells.
They play a role in synaptic pruning during development and memory processing.
When activated, they move towards the affected area to remove foreign invaders or tissue debris by phagocytosis.

Ependymal cells line the internal, fluid-filled cavities of the CNS.
They help form cerebrospinal fluid.
They have cilia that contribute to the flow of cerebrospinal fluid.
They serve as neural stem cells, able to form new neurons and glial cells, especially after injury.

The brain is protected by the absence of a lymphatic system, which is replaced by the glymphatic system.
The glymphatic system facilitates a cleansing fluid exchange within brain spaces.
Astrocytes facilitate this process, which increases during sleep.
The brain is also protected by the myelin sheaths formed by oligodendrocytes around axons.