<prompt> Blood brain barrier is formed byMicrogliaOligodendrocytesAstrocytesType II pneumatocytes  <response>: C Astrocytes Blood Brain Barrier: Astrocytes form the structural framework for the neurons and control their biochemical environment. Astrocyte foot processes are closely associated with the blood vessels to form the blood-brain barrier. Oligodendrocytes are responsible for the formation and maintenance of the myelin sheath, which surrounds axons and is essential for the rapid transmission of action potentials by solitary conduction. Microglia are blood-derived mononuclear macrophages Astrocyte foot processes are closely associated with the blood vessels to form the blood - brain barriers oligodendrocytes forms myelin sheath which surrounds axons. Microglia are blood derived non nuclear macrophages. Blood-brain barrier BBB is a membranic structure that acts primarily to protect the brain from chemicals in the blood, while still allowing essential metabolic function. BBB is composed of endothelial cells, which are packed very tightly in brain capillaries. This higher density restricts passage of substances from the bloodstream much more than endothelial cells in capillaries elsewhere in the body. Astrocyte cell projections called astrocytic feet also known as glial limitans surround the endothelial cells of the BBB, providing biochemical support to those cells. BBB is distinct from the similar blood-cerebrospinal fluid barrier, a function of the choroidal cells of the choroid plexus. 