[pygy_]

As its name implies, the blood brain barrier protects the brain from whatever happens to flow in the blood stream. The herpes virus enters the brain by another channel : the peripheral, somatosensory nerve cells whose axon has a T shape. One prong of the top bar goes to the peripheral tissue, and the other prong goes up to the brainstem.

[dnautics]

thanks for the explanation! That wasn't clear to someone who has enough biochemistry and biology to be dangerous but with no experience in physiology.

[pygy_]

You're welcome!

Expanding further: the blood brain barrier is made of cytoplasmic expansions of astrocytes in the central nervous system. The T-shape sensory cells are part of the peripheral nervous system, their axon ends up in the encephalon.