Glial cell

Glial cells, also called glia, are a component of of the nervous system. They are found in higher numbers than neurons in the human brain, and have many functions depending on the cell type.

All glia do not transmit electrical signals so are insulating. Some glia use this property to provide the insulating layer of myelin around the axons of neurons. Oligodendrocytes provide this insulating layer in the Central Nervous System (CNS). Schwann Cells provide this in the Peripheral Nervous System (PNS). Both types of cell wrap around the axon and produce myelin, a type of electrical insulating plasma membrane. This is a vital component as it provides the mylein sheath which substantially increases the speed at which action potentials are conducted.

Another type of glia, called astrocytes, acts to protect the brain from toxic chemicals. They surround the blood vessels that are very permeable to prevent toxic chemicals from diffusing into these vessels. They do not, however, protect against fat-soluble toxins such as anaesthetics and alcohol, as the glia consist of plasma membrane which is permeable to fat-soluble substances.