Brain vessels enter the central nervous system through holes in the meningeal layers. The cells in the blood vessel walls are joined tightly to one another, forming the blood–brain barrier, which blocks the passage of many toxins and pathogens (though at the same time blocking antibodies and some drugs, thereby presenting special challenges in treatment of diseases of the brain). Neuroanatomists usually divide the vertebrate brain into six main regions: the telencephalon (cerebral hemispheres), diencephalon (thalamus and hypothalamus), mesencephalon (midbrain), cerebellum, pons, and medulla oblongata. Each of these areas has a complex internal structure. Some parts, such as the cerebral cortex
Anatomy of the cerebellum would go to mossy fibers that synapse with granule and Golgi neurons with the granule cells then targeting Purkinje neurons via their excitatory parallel fibers. If the inferior olive it would go via excitatory climbing fiber inputs to Purkinje neurons. These return this output back to the cerebral cortex through the ventrolateral thalamus completing the loop. The corticopontocerebellar pathway is the largest pathway associated with the cerebellum. Arising in the cerebral cortex these fibers first terminate ipsilaterally in the pontine nuclei. Then the fibers decussate and form the middle cerebellar peduncle, terminating in the cerebellar cortex as mossy fibers. This