Description: Professor Saltzman continues his discussion of cell communication in the body, extending the description to the nervous and immune system. Professor Saltzman describes the mode of signal transmission in neurons: action potential in the axon, and neurotransmitter release at the synaptic cleft. He also introduces elements of the innate and adaptive immune system. The adaptive immune system is presented as a host/foreign antigen recognition system involving immune cells (T, B, and macrophages), antibodies, and the major histocompatibility complex 1 and 2. Immune response by cytotoxic T cells, T helper cells, and B cells to antigen recognition are discussed in detail.