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
If We Are the Body the following week. The song re-entered at number 37 for the chart week of September 6, 2003, In its seventh chart week, "If We Are the Body" advanced to number 24 and in its 10th chart week, it advanced to number seven. In its 12th chart week, "If We Are the Body" reached its peak position of number three on the Hot Christian Songs chart. It also peaked at number three on the "Billboard" Hot Christian AC chart and spent three weeks atop both the "Radio & Records" Christian AC and Christian CHR charts. Casting Crowns has performed "If We