B: Blood-brain barrier serves to restrict and control the movement of substances between the general circulation and brain extracellular fluid. A: The Circle of Willis is an arterial polygon formed as the internal carotid and vertebral systems anastomose around the optic chiasm or chiasma (partial crossing of the optic nerve). It provides blood to the brain and neighboring structures. C: Corticobulbar projections have several functions including voluntary control over cranial nerves, relay to the cerebellum, activation of other descending pathways and modulation of sensory processing. D: Lateral corticospinal tract is responsible for controlling the speed and precision of skilled movements of the hands.