neurons, glial cells do not conduct nerve electrical signals. They instead serve to protect and nourish the neurons. Neurons depend on glial cells to grow, nourish themselves, and establish effective synapses. The glial cells of the CNS therefore support the neurons both physically and chemically via processes needed for cell survival. In addition, they maintain and regulate the composition of the fluid surrounding the neurons in the nervous system. This is very important because this environment is highly specialised, and very narrow limits are required for optimal neuronal function. Glial cells also actively participate in enhancing synaptic function. "Astro" means "star" and "cyte" means cell. Astrocytes are so named because they have a star-like shape. They are the most abundant glial cells and have the following crucial functions: They act as a "glue" to hold neurons together in their proper positions They serve as scaffolding to guide neurons to their proper destination during brain development in the foetus They cause the small blood vessels in the brain to change and establish the blood-brain barrier They help in repairing brain injuries and in forming neural scar tissue They play a role in neurotransmitter activity by bringing the actions of some chemical messengers to a halt by taking up the chemicals. They also break down these taken-up chemicals and transform them into raw materials that are used to make more of these neurotransmitters They take up excess potassium ions from brain fluid to help stabilise the ratio between sodium and potassium ions