Batrachotoxin A potent neurotoxin of some South American frogs that has been used as arrow poisons. Benign Tumor A tumor that does not metastasize or invade surrounding tissue. Blood-Brain Barrier The anatomical barrier that isolates the CNS from the general circulation.  The cell responsible is the astrocyte, which forms, layers around capillaries and regulates diffusion of substances from the blood circulation to the neurons. Botulinum toxin A potent neurotoxin that blocks the release of acetylcholine at neuromuscular junctions. b-Bungarotoxin A potent neurotoxin (venom) of elapid snakes that prevents the release of neurotransmitters, thus causing paralysis and death.