Microglial cells are the macrophages of the brain. Their function is not well understood, but they probably contribute to many aspect of regulation of neuronal function, including metabolism of neurotransmitters and myelin turnover. The full extent of microglial cell extension is very difficult to appreciate in the brain. This picture shows an F4/80-positive microglial cell spread in the outer plexiform layer of the retina. This is an en face section of the retina, and the cell spreads essentially in two dimensions in the narrow plexiform layer.