<P> The human brain is primarily composed of neurons, glial cells, neural stem cells, and blood vessels . Types of neuron include interneurons, pyramidal cells including Betz cells, motor neurons (upper and lower motor neurons), and cerebellar Purkinje cells . Betz cells are the largest cells (by size of cell body) in the nervous system . The adult human brain is estimated to contain 86 ± 8 billion neurons, with a roughly equal number (85 ± 10 billion) of non-neuronal cells . Out of these neurons, 16 billion (19%) are located in the cerebral cortex, and 69 billion (80%) are in the cerebellum . </P> <P> Types of glial cell are astrocytes (including Bergmann glia), oligodendrocytes, ependymal cells (including tanycytes), radial glial cells and microglia . Astrocytes are the largest of the glial cells . They are stellate cells with many processes radiating from their cell bodies . Some of these processes end as perivascular end - feet on capillary walls . The glia limitans of the cortex is made up of astrocyte foot processes that serve in part to contain the cells of the brain . </P> <P> Mast cells are white blood cells that interact in the neuroimmune system in the brain . Mast cells in the central nervous system are present in a number of brain structures and in the meninges; they mediate neuroimmune responses in inflammatory conditions and help to maintain the blood--brain barrier, particularly in brain regions where the barrier is absent . Across systems, mast cells serve as the main effector cell through which pathogens can affect the gut--brain axis . </P> <P> Some 400 genes are shown to be brain - specific . In all neurons ELAVL3 is expressed, and in pyramidal neurons NRGN and REEP2 are also expressed . GAD1 essential for the biosynthesis of the neurotransmitter GABA is expressed in interneurons . Proteins expressed in glial cells are astrocyte markers GFAP, and S100B . Myelin basic protein and the transcription factor OLIG2 are expressed in oligodendrocytes . </P>

How many parts of the brain are there and what do they do