Nervous system would not exist without the human brain. Most neurons send signals via their axons, although some types are capable of dendrite-to-dendrite communication. (In fact, the types of neurons called amacrine cells have no axons, and communicate only via their dendrites.) Neural signals propagate along an axon in the form of electrochemical waves called action potentials, which produce cell-to-cell signals at points where axon terminals make synaptic contact with other cells. Synapses may be electrical or chemical. Electrical synapses make direct electrical connections between neurons, but chemical synapses are much more common, and much more diverse in function. At a chemical
Nanoparticles for drug delivery to the brain drug. Bolaamphiphile nano-vesicles can cross the BBB, and they allow controlled release of the drug to target sites. Lipoplexes can also be formed from cationic liposomes and DNA solutions, to yield transfection agents. Cationic liposomes cross the BBB through adsorption mediated endocytosis followed by internalization in the endosomes of the endothelial cells. By transfection of endothelial cells through the use of lipoplexes, physical alterations in the cells could be made. These physical changes could potentially improve how some nanoparticle drug-carriers cross the BBB. Metal nanoparticles are promising as carriers for drug delivery to the brain. Common metals used for nanoparticle