Animation of cells and blood vessels in the brain. Brain cells include the neurons than send and recieve signals, and astrocytes and microglia cells, which provide a supportive and immunological role. The brain is supplied with blood by the cerebral arteries. The blood flow to the brain is separate from the normal circulation by the blood-brain barrier, in which the capillary walls have tight junctions that limit the passage of pathogens and some chemicals across them. This protects the brain from pathogens in the general bloodstream.