Q. What is bathing in Cerebro-Spinal Fluid?

The CNS is bathing in Cerebro-Spinal Fluid (or CSF):  similar to plasma, less protein, rich in ascorbic acid, different in ions Na+ and K+).  If RBCs may indicate meningitis, tumors, MS, ... (spinal tap). 

The Blood Brain barrier (BBB):  no other organ is so dependent on exactly maintaining a constant environment than the brain.  The BBB refers to the fact that cerebral capillaries are least permeable in body.  Only water, amino acids, sugar can freely go in. 

Cranial Nerves: 12 pairs primarily serving the head and neck.  Described by name, number, course, and function.  These include sensory and motor functions. 

Spinal Nerves: 31 pairs. Named for the region of the cord from which they arise.  Each spinal nerve divides into dorsal and ventral branches (or ramifications).