Protection and Nourishment of the Brain

Study Notes

Glial cells make up about 90% of the cells in the central nervous system, but only occupy about half the volume of the brain due to their non-extensive branching.
Glial cells do not initiate or conduct nerve impulses, but are essential for the viability of the central nervous system.
They serve as the connective tissue of the central nervous system, supporting neurons physically and metabolically.

There are four major types of glial cells: astrocytes, oligodendrocytes, ependymal cells, and microglia cells.

Provide critical functions, including:
- Holding neurons together in proper spatial relationship
- Aiding in the repair of brain injuries and neural scar formation
- Supporting neurons metabolically
- Taking up excess potassium from the brain extracellular fluid
Surround brain capillaries with their processes, playing a role in the blood-brain barrier
Have three major roles: signaling cells to form tight junctions, participating in cross-cellular transport, and serving as supporting frameworks

Form insulative myelin sheets around axons in the central nervous system
Have elongated projections that wrap around sections of intraneuronal axons to form patches of myelin

Line the internal cavities of the central nervous system, including the ventricles of the brain and the central canal of the spinal cord
Contribute to the formation of cerebrospinal fluid

Act as scavengers of the central nervous system, removing foreign invaders and tissue debris
Are fibrocystic cells delivered by the blood to the central nervous tissue, remaining stationary until activated by infection or injury
Migrate to affected areas to remove foreign substances

Most brain tumors of neural origin consist of glial cells (gliomas) because they can undergo cell division
Neurons themselves do not form tumors due to their inability to divide and multiply
Brain tumors of non-neuronal origins include:
- Those that metastasize to the brain from other sites
- Meningiomas, which originate from the meninges (protective membrane covering the central nervous system)